Original edge detecting system and optical sensor

ABSTRACT

An original placement table is provided, on which an original sheet is placed. An original scanning device causes a light beam to scan the original sheet placed on the original placement table. A light receiving device receives a light beam which has been reflected by the original sheet placed on the original placement table after being emitted by the original scanning device. An original edge determining device monitors light intensity of the light beam received by the light receiving device. The original edge determining device determines that the light beam currently being received by the light receiving device is the light beam reflected by an edge of the original sheet placed on the original placement table when a significant variation is detected in the light intensity either for the first time or for the last time in one scanning operation of the original scanning device.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an original edge detecting system, inparticular, to an original edge detecting system for detecting edges ofan original paper sheet. The original paper sheet is a sheet of paper,optical information to be processed provided thereon, hereinafter.

Further, the present invention also relates to an optical sensor inwhich a light source emits light on a to-be-detected object, and lightreflected by the to-be-detected object and passing through aretroreflection path is received. Such an optical sensor may be used inthe above-mentioned original edge detecting system.

2. Description of the Related Art

The Japanese Patent Publication No. 59-22992 discloses an informationreading apparatus in which a laser beam is directed on a rotatinghologram disc, forming scan lines, to scan an information carrier. Lightreflected by the information carrier is detected through a photoelectricconverter, and is converted into an electric signal. Thus, informationcarried by the information carrier is read. In the information readingapparatus, the photoelectric converter detects light from theinformation carrier, which light passes a hologram used in the scanningor another hologram having a focus at a position the same as theposition of the focus of the hologram used in the scanning.

The Japanese Laid-Open Patent Application No. 6-242391 discloses alight-scanning original reading apparatus having light scanning meansfor using light for scanning a surface of an original paper sheet, thescanning light being incident on and drawing scan lines on the surfaceof the original paper sheet; means for detecting light reflected anddiffused by the surface of the original paper sheet; and means forcalculating a size and a leaning angle of the original paper sheet frominformation indicating intensity of the detected light and positions ofthe scan lines.

The Japanese Laid-Open Patent Application No. 50-119537 discloses anoptical reading apparatus in which light from a light source scans ato-be-read part so as to result in scanning lines on the to-be-readpart, which scanning lines on the to-be-read part cross each other, andlight reflected by the to-be-read part and passing a path the same as apath which the light passed when it was incident on the to-be-read partis detected. Thus, information is read from the to-be-read part.

In the above-described information reading apparatus disclosed in theJapanese Patent Publication No. 59-22992, it is considered that laserlight is used for the scanning. Thereby, it is possible to obtain a verysmall spot diameter and therefore to read information with a highresolution. However, various images may be present on the original papersheet. Further, a paper pressing sheet which is provided in theapparatus for pressing and thus holding the original paper sheet mayhave dirt adhering thereon. Therefore, it may be difficult to correctlydetect an edge of the original paper sheet. This is because, when alight spot of the very small spot diameter is used, it may be difficultto distinguish light intensity variation occurring when the light spotpasses the edge of the original paper sheet from light intensityvariation occurring when the light spot passes the various imagespresent in the paper sheet or from light intensity variation occurringwhen the light spot passes the dirt adhering on the paper pressingsheet. Therefore, erroneous detection of the edge of the original papersheet may occur. As a result, size detection of an original paper sheetbased on a result of the edge detection of the original paper sheet mayinclude errors.

In other words, only using intensity variation of received light, it maybe difficult to correctly determine whether the received light is lightreflected by an original paper sheet or the paper pressing sheet, orother disturbance light.

Further, images present in the original paper sheet may be erroneouslydetected as the edge of the paper sheet. Thereby, detection of the edgeof original paper sheet may be confused in the apparatus. In order toprevent such a problem due to the contents of the images present in theoriginal paper sheet, a diameter of the scanning light spot may be arelatively larger one. It is possible to have a relatively largerbeam-spot diameter. However, it is advantageous to instead use alight-emitting diode. In fact, when using laser light in a public-useapparatus, it is necessary to provide many safety devices so as tofulfill many safety regulations. Further, it is likely that a systemusing laser light is adversely affected by electric noise, driving ofthe system is relatively difficult, and the system is relatively costly.

A case may be considered in which a light-emitting diode is combinedwith the above-mentioned hologram in the information reading apparatusdisclosed in the Japanese Patent Publication No. 59-22992. However, inthis case, light passing through the hologram may have a very longsectional shape due to diffusion occurring when an optical path is long.Thereby, resolution may be too low to perform an effective function.Thus, it may be difficult to apply a light-emitting diode, which is easyto handle, in the disclosed method.

In the above-described light-scanning original reading apparatusdisclosed in Japanese Laid-Open Patent Application No. 6-242391, lightfrom the light source is used to scan the surface of the original papersheet. Using an intensity of light reflected, it is distinguishedwhether the light is reflected by the paper sheet or by another surface.However, various images may be present on the original paper sheet, asmentioned above. As a result, there is a possibility that a sharpvariation in light intensity occurring when the light scans an imagepresent on the original paper sheet is erroneously recognized to be asharp variation in light intensity occurring when the light scans anedge of the paper sheet.

Further, the above-described optical reading apparatus disclosed in theJapanese Laid-Open Patent Application No. 50-119537 uses laser light.Therefore, as described above, it is necessary to provide many safetydevices, it is likely that a system using laser light is adverselyaffected by electric noise, and driving of the system costs much.

An optical sensor such as that mentioned above is used to detect a sizeand/or a position of an original paper sheet of a copying machine, forrecognizing information provided on articles such as bar codes, fordetecting articles in a factory, and so forth.

For example, the above-described light-scanning original readingapparatus disclosed in the Japanese Laid-Open Patent Application No.6-242391 uses an optical sensor using a semiconductor laser forproducing a laser beam in the above-mentioned light-scanning means in anoptical sensor.

Further, the Japanese Patent Publication No. 53-42576 discloses anoptical reading apparatus using an optical sensor in which laser lightemitted by a laser oscillator is caused to pass through a center of amirror having an opening. Then, the light is used to scan a to-be-readpart through a plurality of deflection mirrors. Then, light reflected bythe to-be-read part and passing a path the same as a path which thelight passed when it was used for the scanning is reflected by a rearsurface of the mirror having the opening. The light reflected by therear surface of the mirror having the opening is received by aphotoelectric converter and converted into an electric signal. Thus,information of the to-be-read part is read.

As described above, laser light is used to scan a to-be-detected objectin each of the above-mentioned optical sensors. A reason for using laserlight is to reduce a spot diameter formed on a to-be-detected object.However, as mentioned above, in order to use laser light in a public-useapparatus, it is necessary to provide many safety devices for fulfillingmany safety regulations. As a result, the apparatus is costly and has alarge size.

In order to eliminate such problems, a laser light source in a lightscanning system in the related art can be replaced with apoint-light-source light-emitting diode having a diameter of alight-emitting area not longer than 0.05 mm for obtaining an appropriatescanning-beam diameter. However, there are few manufacturers whichprovide such point-light-source light-emitting diodes, and suchpoint-light-source light-emitting diodes are costly in comparison toordinary light-emitting diodes. Further, because frequencies which canbe used in such point-light-source light-emitting diodes are limited, itis not possible to actually use them for the above-mentioned purpose.Because each of ordinary, non-expensive light-emitting diodes on themarket has a large light-emitting area of 0.3 mm, it is not possible toreplace the laser light source in the light scanning system in therelated art with a light-emitting diode.

SUMMARY OF THE PRESENT INVENTION

An original edge detecting system according to the present inventioncomprises:

an original placement table, on which an original paper sheet is placed;

original scanning means for causing a light beam to scan the originalpaper sheet placed on the original placement table;

light receiving means for receiving a light beam which has beenreflected by the original paper sheet placed on the original placementtable after being emitted by the original scanning means; and

original edge determining means for monitoring light intensity of thelight beam received by the light receiving means,

the original edge determining means determining that the light beamcurrently being received by the light receiving means is a light beamreflected by an edge of the original paper sheet placed on the originalplacement table when a sharp variation is detected in the lightintensity either for the first time or for the last time in one scanningoperation of the original scanning means.

Thereby, edges of the original paper sheet can be suitably detectedwithout being affected by an optical density of an image provided on theoriginal paper sheet. As a result, a size of the original paper sheetcan be correctly detected.

The original edge detecting system may further comprise an originalpressing sheet for having the original paper sheet inserted between theoriginal pressing sheet and the original placement table,

wherein:

one of the original pressing sheet and the original placement table issubstantially transparent, and through the transparent one the originalscanning means causes the light beam to scan the original paper sheetinserted between the original pressing sheet and the original placementtable; and

a diameter of a cross section of the light beam emitted by the originalscanning means is, at an incident surface of the original paper sheet,larger than an interval of dirty spots which possibly occur at intervalson the other one of the original pressing sheet and the originalplacement table.

Thereby, ripples possibly included in a waveform of intensity ofreceived light due to the dirty spots at the intervals can beeffectively eliminated. Thus, it is possible to cause a clear differenceto appear between a received light intensity waveform resulting frombeing reflected by an edge of the original paper sheet and a receivedlight intensity waveform resulting from being reflected by possibledirty spots at the intervals on the original pressing sheet. As aresult, it is possible to suitably process an output signal from thelight receiving means, and thus to precisely, easily recognize edges ofthe original paper sheet.

The original edge detecting system may further comprise thresholdsetting means for setting a threshold value with which the original edgedetermining means determines whether or not the light beam currentlybeing received by the light receiving means is the light beam reflectedby the edge of the original paper sheet placed on the original placementtable,

the threshold setting means setting the threshold value using adifference in the light intensity of the light beam received by thelight receiving means when the sharp variation occurs in the receivedlight intensity for the first time in the first scanning of the originalpaper sheet.

Thereby, the threshold value appropriate for a particular reflectivityof the original paper sheet can be automatically set. As a result, asize of the original paper sheet can be detected without being affectedby a particular optical density of the original paper sheet.

It may be that:

the original scanning means uses a light-emitting diode as a lightsource of the light beam, and a single lens for converging the lightbeam on the original paper sheet,

a ratio of a diameter of a light-emitting surface of the light-emittingdiode to a diameter of a cross section of the light beam at a surface ofthe original paper sheet being approximately equal to a ratio of anoptical-path length between the light-emitting diode and the single lensto an optical-path length between the single lens and the original papersheet; and

a beam splitter is located in a course of a retroreflection path betweenthe surface of the original paper sheet and the light-emitting diode,the beam splitter partially reflecting light which has been reflected bythe original paper sheet,

the light receiving means, which receives light reflected by the beamsplitter, being located at a position which is an approximatelyconjugate converging point with respect to the surface of the originalpaper sheet.

By making the ratio of the diameter of the light-emitting surface of thelight-emitting diode to the diameter of the cross section of the lightbeam at the surface of the original paper sheet approximately equal tothe ratio of the optical-path length between the light-emitting diodeand the single lens to the optical-path length between the single lensand the original paper sheet, the light emitted by the light-emittingdiode is incident on the original paper sheet with a desired light-spotdiameter. The light reflected by the original paper sheet returns alongthe scanning light path and then is partially reflected by the beamsplitter. Thus, the reflected light from the original paper sheet has adesired focus on the light receiving means, while reflected light fromthe other objects does not have a desired focus on the light receivingmeans. Thus, it is possible to clearly distinguish the light reflectedby the original paper sheet from the light reflected by the otherobjects, and thus to precisely detect edges of the original paper sheet.

Further, in order to obtain an optical light-beam diameter and anoptical light intensity of light incident on the light receiving meansfrom the original paper sheet and original pressing sheet through thecompact retroreflection path, the light-emitting diode, single lens andbeam splitter are necessary. By using the beam splitter, in particular,it is possible to obtain a compact, high-performance sensor. This isbecause, in order to obtain an appropriate light-beam diameter using anordinary light-emitting diode with high light-using efficiency, it isnecessary to split the incident light from the reflected light in acondition in which a diameter of the light beam is large. Each of a beamsplitter and a diffraction grating can achieve this splitting in theretroreflection path. However, if the diffraction grating is used, thelight from the light-emitting diode disperses and does not converge. Incontrast to this, the beam splitter is preferable in this purposebecause the light emitted by the light-emitting diode converges.Therefore, an inexpensive combination of the light-emitting diode whichis easy to drive and the single lens can be used for the light-beamscanning operation on the original paper sheet in the high-performanceoptical sensor.

The original edge detecting system may further comprises convergingmeans, in addition to the single lens, for converging the light beamemitted by the light-emitting diode, the light beam being incident onthe single lens after converging through the converging means. Thereby,diffusing light emitted by the light-emitting diode can be effectivelycollected and efficient use of the light beam emitted by thelight-emitting diode can be achieved.

It may be that the light receiving means is provided at an arbitraryposition but out of an optical path along which the light beam emittedby the light-emitting diode extends to the original paper sheet; and

the light receiving means serves a wide-angle light receiving functionand thus receives light reflected by the entirety of the scanningsurface.

Thereby, the reflected light from the above-mentioned original placementtable does not pass the scanning optical path and is received by thelight receiving means. Thus, the light receiving means can be located atan arbitrary position.

Another original edge detecting system according to the presentinvention comprises:

a transparent original placement table;

an original pressing sheet for overlying the original placement table;

light scanning means for scanning an original sheet on the originalplacement table through the original placement table with a light beam;

distance-detection light-receiving means for outputting a signalaccording to a length of incident-light path when receiving a lightreflected by the original sheet; and

original edge determining means which uses the signal output by thedistance-detection light-receiving means, determines whether a lightcurrently incident on the distance-detection light-receiving means is alight reflected by the original sheet, and determines positions of edgesof the original sheet.

Thereby, although various lights such as those from the original sheetand the original pressing sheet, a disturbance light, and so forth, areincident on the distance-detection light-receiving means, by recognizinga length of the incident-light path through the distance-detectionlight-receiving means, it is possible to positively distinguish thelight reflected by the original sheet from the others. As a result,during a scanning operation of the light scanning means, it is possibleto determine that the light currently incident on the distance-detectionlight-receiving means is a light reflected by the original sheet even ifthere is no effective light intensity difference between a case wherethe light currently incident is a light reflected by the original sheetand other cases. Thereby, together using information of a scanningoperation timing of the light scanning means, it is possible toprecisely detect positions of edges of and, thereby, also a size of andan inclination of the original sheet.

In the original edge detecting system, it may be that:

the distance-detection light-receiving means comprises a plurality oflight receiving areas arranged symmetrically with a symmetrical centercorresponding to a center of the distance-detection light-receivingmeans; and

a knife edge is provided in front of the distance-detectionlight-receiving means.

In this arrangement, according to the principle of the well-known knifeedge method, the length of the incident-light path through thedistance-detection light-receiving means can be recognized.

Instead, in the original edge detecting system, it may be that:

the distance-detection light-receiving means comprises a central lightreceiving area located in a center of the distance-detectionlight-receiving means and a peripheral light-receiving area locatedperipheral of the central light receiving area.

In this arrangement, according to the principle of the well-known beamsize method, the length of the incident-light path through thedistance-detection light-receiving means can be recognized.

Instead, in the original edge detecting system, it may be that:

the distance-detection light-receiving means comprises at least fourlight receiving areas arranged symmetrically with a symmetrical centercorresponding to a center of the distance-detection light-receivingmeans; and

a focal lens for converging an incident light and a cylindrical lens ora wedge prism are provided in front of the distance-detectionlight-receiving means.

In this arrangement, according to the principle of the well-knownastigmatic method, the length of the incident-light path through thedistance-detection light-receiving means can be recognized.

Instead, in the original edge detecting system, it may be that:

the distance-detection light-receiving means comprises aposition-detection sensor which has a two-dimensional light receivingarea; and

a size, a shape, a light-intensity distribution or the like of areceiving light spot formed on the position-detection sensor varies as alength of an incident-light path from a point at which the light isreflected after being incident at the point as a result of a scanningoperation by the light-scanning means.

In this arrangement, the length of the incident-light path through thedistance-detection light-receiving means can be recognized through theposition-detection sensor.

Instead, in the original edge detecting system, it may be that:

the distance-detection light-receiving means comprises a CCD sensorwhich has a two-dimensional light receiving area; and

a size, a shape, a light-intensity distribution or the like of areceiving light spot formed on the position-detection sensor varies as alength of an incident-light path from a point at which the light isreflected after being incident at the point as a result of a scanningoperation by the light-scanning means.

In this arrangement, the length of the incident-light path through thedistance-detection light-receiving means can be recognized through theCCD sensor.

In the original edge detecting system, it may be that:

the distance-detection light-receiving means comprises a plurality oflight receiving areas;

a predetermined bias component is subtracted from an output of a firstone of the plurality of light receiving areas;

a predetermined bias component is subtracted from an output of a secondone of the plurality of light receiving areas;

a result of subtracting the predetermined bias component from the outputof the second one of the plurality of light areas is multiplied with apredetermined coefficient; and

whether a light currently incident on the distance-detectionlight-receiving means is one reflected by the original sheet isdetermined by comparing a result of subtracting the predetermined biascomponent from the output of the first one of the plurality of lightreceiving areas with a result of the multiplication using thepredetermined coefficient.

When a disturbance light incident on the distance-detectionlight-receiving means is a light from the sun, the light intensity ofthe incident light is so strong that the above-mentioned difference isextremely large. In contrast to this, there is a case where thedisturbance light is a light produced in an ordinary office roomenvironment. In such a case, if the distance-detection light-receivingmeans has split or a plurality of light receiving areas such as thoseshown in FIGS. 17A-17C, there is a tendency that light is uniformlyincident on the split or plurality of light receiving areas when thelength of the incident-light path is relatively long. Therefore, thereare only small differences between outputs from the light receivingareas. In such a case, the bias components substantially adverselyaffect the above-mentioned distance determination. Therefore,subtracting the bias components from the outputs of the light receivingareas is advantageous.

In the original edge detecting system, a light-emitting diode may beused as a light source of the light scanning means. Thereby, it ispossible to effectively reduce costs of the original edge detectingsystem.

An optical sensor according to the present invention comprises:

a light scanning mechanism which causes light emitted by alight-emitting diode to scan for a to-be-detected object;

a converging optical system which causes the light emitted by thelight-emitting diode to converge on the to-be-detected object; and

a beam splitter which partially reflects the light which has beenreflected by the to-be-detected object, the reflected light beingincident on light receiving means.

In this sensor, the light emitted by the light-emitting diode is causedto converge through the converging optical system and is used for thescanning operation for the to-be-detected object. The light reflected bythe to-be-detected object returns along a retroreflection path the sameas a scanning optical path. Then, the light is partially reflected bythe beam splitter and the reflected light is incident on the lightreceiving means. Thus, by detecting variation in intensity of lightreceived by the light receiving means, the presence of theto-be-detected object is detected.

In this arrangement, the inexpensive light-emitting diode, which iseasily driven and for which any extra provision for fulfilling safetyregulations is not needed, can be used. Thus, costs are effectivelylowered.

The optical sensor may further comprise another converging opticalsystem which causes the light reflected by the beam splitter to convergeon the light receiving means. As a result, separate converging opticalsystems are used for the light emitted by the light-emitting diode andincident on the to-be-detected object and the light reflected by theto-be-detected object and incident on the light receiving unit,respectively. As a result, it is possible to use a lens havingcharacteristics of a high value of NA (Numerical Aperture) as theconverging optical system for the light emitted by the light-emittingdiode and incident on the to-be-detected object. Thereby, it is possibleto enhance light intensity of light being incident on the to-be-detectedobject. Further, the converging optical system for the light reflectedby the to-be-detected object and incident on the light receiving unit isprovided such that only the light reflected by the to-be-detected objecthas a desired focus on the light receiving means and light reflected bythe other objects does not have a desired focus on the light receivingmeans. Thus, it is possible to improve an accuracy in detecting theto-be-detected object.

The converging optical system may further cause the light reflected bythe beam splitter to converge on the light receiving means. Thereby, thecommon converging optical system is used for both the light emitted bythe light-emitting diode and incident on the to-be-detected object andthe light reflected by the to-be-detected object and incident on thelight receiving unit. Thereby, it is possible to effectively lower costsand also miniaturize the optical sensor.

Another optical sensor according to the present invention comprises:

a light scanning mechanism which causes light emitted by alight-emitting diode to scan for a to-be-detected object;

a first converging optical system which causes the light emitted by thelight-emitting diode to converge on the to-be-detected object; and

a second converging optical system which causes the light reflected bythe to-be-detected object to converge on light receiving means;

wherein the second converging optical system is located in a reflectingoptical path along which the light reflected by the to-be-detectedobject extends, the reflecting optical path being different from ascanning optical path along which the light emitted by thelight-emitting diode extends to the to-be-detected object.

Thereby, by using the inexpensive light-emitting diode on the market, adesired light-spot diameter appropriate for the to-be-detected objectcan be obtained. Further, the light reflected by the to-be-detectedobject is neither partially reflected nor split by, for example, thebeam splitter. As a result, it is possible to efficiently use the lightfrom the light-emitting diode.

Other objects and further features of the present invention will becomemore apparent from the following detailed description when read inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B show a general arrangement and a block diagram,respectively, of an original reading apparatus in a first embodiment ofthe present invention;

FIG. 2 illustrates a spatial relationship between an original papersheet and a scan line in the apparatus shown in FIGS. 1A and 1B;

FIG. 3 shows a graph indicating variation of received light intensity ona light receiving unit in an original reading apparatus in a secondembodiment of the present invention;

FIG. 4 shows an optical path arrangement from a light-emitting diode toa surface of an original paper sheet in the original reading apparatusin the second embodiment of the present invention;

FIG. 5A shows a block diagram of an original reading apparatus in athird embodiment of the present invention;

FIG. 5B illustrates an operation of the apparatus shown in FIG. 5A.

FIG. 6 shows a light beam in a scanning optical path in an originalreading apparatus in a fourth embodiment of the present invention;

FIG. 7 shows an optical path arrangement in the original readingapparatus in the fourth embodiment of the present invention;

FIG. 8 shows a perspective view of a mirror in a deflecting unit forillustrating a deflection function in the original reading apparatus inthe fourth embodiment of the present invention;

FIG. 9 shows another optical path arrangement in the original readingapparatus in the fourth embodiment of the present invention;

FIG. 10 shows an optical path arrangement in an original readingapparatus in a fifth embodiment of the present invention, showing ascanning optical path from a light-emitting diode to a scanning surfaceand a reflecting optical path from the scanning surface to a lightreceiving unit;

FIG. 11 shows an optical path arrangement in an original readingapparatus in a sixth embodiment of the present invention, showing ascanning optical path from a light-emitting diode to a scanning surfaceand a reflecting optical path from the scanning surface to a lightreceiving unit;

FIG. 12 illustrates a seventh embodiment of the present invention;

FIGS. 13A-13C illustrate variation of a spot formed on adistance-detection light-receiving unit obtained as a length of anincident-light path varies in the embodiment shown in FIG. 12;

FIG. 14 illustrates an eighth embodiment of the present invention;

FIGS. 15A-15C illustrate variation of a spot formed on adistance-detection light-receiving unit obtained as a length of anincident-light path varies in the embodiment shown in FIG. 14;

FIG. 16 illustrates a ninth embodiment of the present invention;

FIGS. 17A-17C illustrate variation of a spot formed on adistance-detection light-receiving unit obtained as a length of anincident-light path varies in the embodiment shown in FIG. 16;

FIG. 18 illustrates a variation example of the ninth embodiment shown inFIG. 16;

FIG. 19 illustrates a tenth embodiment of the present invention;

FIG. 20 shows a perspective view indicating a spatial relationshipbetween a light scanning unit and a position-detection sensor in thetenth embodiment;

FIG. 21 illustrates variation of a spot formed on a position-detectionsensor obtained as a length of an incident-light path varies in thetenth embodiment shown in FIG. 19;

FIG. 22 illustrates an eleventh embodiment of the present invention;

FIGS. 23A and 23B illustrate a twelfth embodiment of the presentinvention, FIG. 23A shows a light path when an incident-light pathlength is relatively short, and FIG. 23B shows a shape of a spot in thecondition shown in FIG. 23A;

FIGS. 24A and 24B show a light path when an incident-light path lengthis relatively long, and a shape of a spot in the condition shown in FIG.24A, respectively, in the twelfth embodiment;

FIGS. 25A, 25B and 25C show a thirteenth embodiment of the presentinvention, FIG. 25A showing an example using a collimator lens, FIG. 25Bshowing an example using an aperture and FIG. 25C showing alight-intensity distribution in a spot on an original paper sheet or anoriginal pressing sheet in the arrangement shown in FIG. 25A or 25B;

FIG. 26A shows a light path when an incident-light path length isrelatively short in the arrangement shown in FIGS. 25A or 25B;

FIG. 26B shows a light-intensity distribution in a spot in the conditionshown in FIG. 26A;

FIG. 26C shows a light path when an incident-light path length isrelatively long in the arrangement shown in FIG. 25A or 25B;

FIG. 26D shows a light-intensity distribution in a spot in the conditionshown in FIG. 26C;

FIG. 27 illustrates a fourteenth embodiment of the present invention,and shows a relationship between a value A-αB (obtained from outputs ofa distance-detection light-receiving unit and a length of anincident-light path;

FIG. 28 shows an optical path arrangement in an optical sensor in afifteenth embodiment of the present invention;

FIG. 29 shows a perspective view of the optical sensor shown in FIG. 28;

FIG. 30 shows a light converging condition from a light-emitting diodeto a to-be-detected object;

FIG. 31 shows an optical path arrangement in an optical sensor in asixteenth embodiment of the present invention;

FIG. 32A shows an optical path arrangement in an optical sensor in aseventeenth embodiment of the present invention; and

FIG. 32B illustrates an operation of the seventeenth embodiment of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to FIGS. 1A, 1B and 2, a first embodiment of the presentinvention will now be described. FIG. 1A shows a general arrangement ofan original reading apparatus in the first embodiment of the presentinvention. The original reading apparatus may have an arrangement suchas that shown in each of FIGS. 12, 14, 16 which will be described laterfor other embodiments of the present invention.

In the original reading apparatus, a light scanning unit 2 is providedinside a body 1 and emits a light beam 6. Above the light scanning unit2, a transparent original placement table (contact glass) 3 on which anoriginal paper sheet is placed is provided. Further, an originalpressing sheet 4 is provided above the original placement table 3 androtatably supported at the left end thereof in FIG. 1A. Thereby, theoriginal pressing sheet 4 can be opened, as shown in FIG. 1A, so that auser can place an original paper sheet on the original placement table3. The original pressing sheet 4 can be closed so that the originalpressing sheet 4 is placed on the original placement table 3, such thatan original paper sheet previously placed on the original placementtable 3 is placed between the original pressing sheet 4 and the originalplacement table 3. Such a mechanism of the original placement table 3and the original pressing sheet 4 for an original paper sheet iswell-known as a mechanism of an ordinary copying machine on the market.The light scanning unit 2 causes the emitted light beam 6 to scan theoriginal paper sheet placed on the original placement table 3 and theinner surface of the original pressing sheet 4.

An original paper sheet 5 (not shown in FIG. 1A but shown in FIGS. 1Band 2) is placed on the original placement table 3. As shown in FIG. 1B,the original reading apparatus further includes a light receiving unit12 which receives the light beam 6, which has been emitted by the lightscanning unit 2 and then reflected by the original paper sheet 5 and theoriginal pressing sheet 4. The original reading apparatus furtherincludes a scanning period signal outputting unit 122. The scanningperiod signal outputting unit 122 outputs a scanning period signal for aperiod of each scanning operation performed by the light scanning unit2.

The original reading apparatus further includes an original edgedetermining unit 123. The original edge determining unit 123 monitors anintensity of the light beam 6 received by the light receiving unit 12.The scanning period signal output by the scanning period signaloutputting unit 122 is used for the original edge determining unit 123to define a duration of one scanning operation. The original edgedetermining unit 123 determines that the light beam 6 received by thelight receiving unit 12 is a light beam reflected by an edge of theoriginal paper sheet 5 when the intensity of the received light beam 6sharply increases or sharply decreases for the first time or for thelast time in the above-mentioned duration of one scanning operation.

An arrow shown in FIG. 2 represents a scanning direction of a scan lineresulting from a movement of a spot 6A of the light beam 6 formed on theinner surface of the original pressing sheet 4 and the original papersheet 5 by the light beam 6 emitted by the light scanning unit 2.

The light scanning unit 2 includes a light-emitting diode (not shown inthe figures) which emits the light beam 6. A going direction of theemitted light beam 6 is deflected by a rotating deflecting member suchas a polygon mirror and thereby the light beam scans the bottom surfaceof the original paper sheet 5.

The above-mentioned scanning period signal outputting unit 122 includesa detector, which detects part of the light beam 6 reflected by theabove-mentioned rotating deflecting member, includes a light receivingsensor which is provided at a portion of the rotating deflecting memberand detects a light beam emitted by the light-emitting diode in thecourse of each scanning operation, or includes means for obtaining areference signal from a control signal which controls a motor drivingthe rotating deflecting member. Thereby, the scanning period signaloutputting unit 122 outputs the scanning period signal for the period ofeach scanning operation.

In the above-described original reading apparatus, the size of theoriginal paper sheet 5 placed on the original placement table 3 is readin a condition in which the original pressing sheet 4 is in a somewhatopen state. Therefore, the light beam 6 emitted by the light scanningunit 2 is incident on the original paper sheet 5 placed on the originalplacement table 3 and other things. As a light, the light receiving unit12 receives light reflected by the original paper sheet 5 and the innersurface of the original pressing sheet 4. Further, because the originalpressing sheet 4 is in the somewhat open state, as mentioned above, thelight receiving unit 2 also receives external light.

It is necessary to read the size of the original paper sheet 5 in acondition in which the original pressing sheet 4 is in a somewhat openstate as mentioned above. This is because, when this size readingoperation is performed in a condition in which the original pressingsheet 4 completely overlies and in contact with the original paper sheet5 and the original placement table 3, it is difficult to distinguishbetween light reflected by the original paper sheet 5 and lightreflected by the original pressing sheet 4.

In this condition in which the original pressing sheet 4 is in thesomewhat open state, the light beam 6 reflected by the inner surface ofthe original pressing sheet 4 is diffused. Thereby, the intensity of thelight beam 6 reflected and then received by the light receiving unit 12is not high. However, in contrast to this, because approximately theentirety of the surface of the original paper sheet 5 is in contact withthe original placement table 3, the light beam 6 reflected by theoriginal paper sheet 5 has a high intensity. By detecting such adifference between these intensities of the received light beam 6, it ispossible to determine, through the original edge determining unit 123,that the light beam 6 emitted by the light scanning unit 2 is incidentat an edge of the paper sheet 5.

As mentioned above, the scanning period signal outputting unit 122outputs the scanning period signal to the original edge determining unit123. Thereby, the original edge determining unit 123 can recognize aperiod of each scanning operation of the light scanning unit 2. Thereby,as described above, the original edge determining unit 123 determinesthat the light beam 6 received by the light receiving unit 12 is thelight beam 6 reflected by an edge of the original paper sheet 5 whenintensity of the received light beam 6 sharply increases or sharplydecreases for the first time or for the last time of the above-mentionedduration of one scanning operation.

The scanning period signal is output, during each of repetitious lightbeam 6 scanning operations, when the light beam 6 passes through an edgeof the transparent original placement table 3, from which edge the lightbeams 6 starts scanning the transparent original placement table 3during each of the repetitious light beam 6 scanning operations. A clocksignal is used in the original edge determining unit 123 and the edgedetermining unit 123 starts counting clock pulses of the clock signalwhen the scanning period signal outputting unit 122 outputs the scanningperiod signal. When the original edge determining unit 123 determinesthat the light currently being received is light reflected by an edge ofthe original paper sheet 5, the current count value of the counting ofthe clock pulses of the clock signal is stored. The stored count valueis used as data indicating positions of starting and ending edges of theoriginal paper sheet 5 placed on the original placement table 3.

Actually, for example, the scanning operation is repeated approximatelyten times per one second and the original-paper-sheet size readingoperation is performed for one or two seconds.

There may be a case where the original paper sheet 5 is generally whiteand therefore has a high reflectivity, for example. In such a case,after one scanning operation is started and the scanning period signalis output by the scanning period signal outputting unit 122, theintensity of the light beam 6 received by the light receiving unit 12sharply increases within a fixed time duration for the first timeresponding to the light beam 6 reaching the starting edge of theoriginal paper sheet 5. This sharp increase in light intensity occurswhen the light beam 6 emitted by the light scanning unit 2 is incidenton the starting edge of the original paper sheet 5 having the highreflectivity placed on the original placement table 3. The light beam 6is thus first incident on the original paper sheet 5 via the transparentoriginal placement table 3. By detecting this sharp increase in lightintensity, the original edge determining unit 123 can determine that thelight beam 6 emitted by the light scanning unit 2 is incident on theedge of the original paper sheet 5.

Further, after that, intensity of light beam received by the lightreceiving unit 12 sharply decreases within a fixed time duration for thelast time during the current scanning operation. This sharp decrease inlight intensity occurs when the light beam 6 emitted by the lightscanning unit 2 has passed across the other edge or the ending edge ofthe original paper sheet 5 placed on the original placement table 3, andthus the light beam 6 has passed across the original paper sheet 5. Bydetecting this sharp decrease in light intensity, the original edgedetermining unit 123 can determine that the light beam emitted by thelight scanning unit 2 has been incident on the other edge or the endingedge of the original paper sheet 5.

There may be another case where the original paper sheet 5 is generallyblack and thus has a low reflectivity. In such a case, after onescanning operation has been started and the scanning period signal isoutput by the scanning period signal outputting unit 122, intensity of alight beam received by the light receiving unit 12 sharply decreaseswithin a fixed time duration for the first time. This sharp decrease inlight intensity occurs when the light beam 6 emitted by the lightscanning unit 2 is incident on the starting edge of the original papersheet 5 having the low reflectivity placed on the original placementtable 3, and the light beam 6 is thus incident on the original papersheet 5 for the first time. By detecting this sharp decrease in lightintensity, the original edge determining unit 123 can determine that thelight beam 6 emitted by the light scanning unit 2 is incident on thestarting edge of the original paper sheet 5.

Further, after that, the intensity of the light beam 6 received by thelight receiving unit 12 sharply increases within a fixed time durationfor the last time during the current scanning operation. This sharpincrease in light intensity occurs when the light beam 6 emitted by thelight scanning unit 2 has passed across the other edge or the endingedge of the original paper sheet 5 having the low reflectivity placed onthe original placement table 3, and thus the light beam 6 has passedacross the original paper sheet 5. By detecting this sharp increase inlight intensity, the original edge determining unit 123 can determinethat the light beam 6 emitted by the light scanning unit 2 has beenincident on the other edge or the ending edge of the original papersheet 5.

Thus, the original edge determining unit 123 only detects such sharpincrease and decrease in light intensity of the received light beam 6for the first time and for the last time after receiving the scanningperiod signal from the scanning period signal outputting unit 122. Forthis purpose, the original edge determining unit 123 should ignore arelatively gentle variation in light intensity as a result of, forexample, a light beam 6 emitted by the light scanning unit 2 beingreflected by the inner surface of the original pressing sheet 4. Asignal processing for obtaining such an effect can be easily embodied.For example, by providing a differentiating circuit, only a differentialcoefficient of intensity of light beam 6 received by the light receivingunit 12, having an amount not less than a fixed value, is maintained.

There may be various images provided on the original paper sheet 5,having various patterns of reflectivity variation, and thereby variousvariations in the intensity of light beam 6 reflected by the variousimages. However, as described above, the original edge determining unit123 ignores any intermediate variation in the intensity of the lightbeam 6 received by the light receiving unit 12 other than the sharpincrease or sharp decrease for the first time and sharp increase orsharp decrease for the last time in the intensity of the light beam 6received by the light receiving unit 12 in one scanning operation.Thereby, it is possible to correctly recognize edges of an originalpaper sheet 5 without the recognition being affected by the contents ofimages present on the original paper sheet 5.

As described above, the original edge determining unit 123 determinesthat a light beam 6 currently received by the light receiving unit 12 isa light beam reflected from an edge of an original paper sheet 5 when asharp increase or a sharp decrease in light intensity of the receivedlight beam 6 for the first time and for the last time after receivingthe scanning period signal from the scanning period signal outputtingunit 122 is detected. For this purpose, an electrical or optical filteror the like is used for previously eliminating influence by disturbancelight. Thereby, the original edge determining unit 123 uses only a lightcomponent corresponding to the light beam 6 which is emitted by thelight scanning unit 2 and then reflected by either the original papersheet 5 or the original pressing sheet 4.

The original reading apparatus in a second embodiment of the presentinvention will now be described with reference to FIGS. 3 and 4. Forcomponents identical to those in the above-described first embodiment,the same reference numerals are given and descriptions therefor areomitted. (A similar manner will be applied to descriptions of subsequentthird, fourth, fifth and sixth embodiments.) The original readingapparatus in the second embodiment also has the structure shown in FIGS.1A and 1B.

Generally speaking, the inner surface of the original pressing sheet 4is white, but likely to be dirty. Further, in many cases, the innersurface of the original pressing sheet 4 is uneven at approximately 1-mmintervals. As a result, when the inner surface is dirty, there are dirtyspots appearing at the same 1-mm intervals. Optical data of these dirtyspots are also input to the light receiving unit 12 and reflectivityvariation due to a dirty spot of the inner surface of the originalpressing sheet 4 may be erroneously recognized as that of an edge of anoriginal paper sheet 5. In order to eliminate such influence due to thedirty inner surface of the original pressing sheet 4, a diameter of thelight beam 6 on an original paper sheet 5 placed on the originalplacement table 3 is determined to be not less than 2 mm. If the lightbeam 6 has an elliptic cross-section, the shortest diameter thereofshould be not less than 2 mm.

In Japan, there are many standard paper sheet sizes such as A-seriessizes and B-series sizes, and there are many standard paper sheet sizesfor paper sheets used for a computer operation. Further, in othercountries, there are other standard paper sheet sizes such as thosebased on the inch unit. In order to identify these standard paper sheetsizes through a single detecting device or a single computer software,it is necessary to recognize a minimum 6-mm space. In order to clearlyidentify a size of an original paper sheet 5, it is necessary that awaveform of the intensity of the light beam 6 received by the lightreceiving unit 12 does not include ripples. For this purpose, it isnecessary to make the diameter of the light beam 6 on the original papersheet 5 small. Consequently, the diameter of the light beam 6 on theoriginal paper sheet 5 placed on the original placement table 3 isdetermined, in a case where the light beam 5 is a circular-cross-sectionlight beam, to be not less than 2 mm and not more than 20 mm. In a casewhere the light beam 5 is an elliptic-cross-section light beam, theshortest diameter thereof should be not less than 2 mm and not more than20 mm.

Further, in order to efficiently narrow light reflected by either theoriginal paper sheet 5 or the original pressing sheet 4 and to cause itto be incident to the light receiving unit 12, as shown in FIG. 4, alight-emitting point P1 (a light-emitting diode 8 in the light scanningunit 2) and a scanning point P2 (on the original paper sheet 5 placed onthe original placement table 3) are approximately conjugate with oneanother. (In the this specification, the term `conjugate` refers to`conjugate in the geometrical optics field`.) In the light scanning unit2, the light beam 6 emitted by the light-emitting diode 8 convergesthrough a single lens 9, and a deflecting unit 10 deflects the lightbeam 6 so as to cause the light beam 6 to scan either the original papersheet 5 or the original pressing sheet 4. The deflecting unit 10 is madeof, for example, a mirror or a prism and a motor which drives the mirroror prism.

Thus, in the original reading apparatus in the second embodiment of thepresent invention, a general pattern of dirt possibly occurring on theinner surface of the original pressing sheet 4 is assumed. Thus, from athus-assumed general distance between adjacent dirty spots, either thediameter of a circular-cross-section light beam 6 on a scanning surface(that is, a surface scanned by the light beam 6) is to be not less than2 mm, or the shortest diameter of an elliptic-cross-section light beamon the scanning surface is to be not less than 2 mm. The light receivingunit 12 has, incident thereon, not only light reflected by an originalpaper sheet 5 but also light reflected by the inner surface of theoriginal pressing sheet 4. However, even if the inner surface of theoriginal pressing sheet 4 has dirty spots occurring thereon atapproximately 1-mm intervals, by using the light beam 6 having thecross-section diameter not less than 2 mm on the scanning surface, awaveform of the intensity of the light beam 6 received by the lightreceiving unit 12 after being reflected by the dirty inner surface ofthe original pressing sheet 4 is smoothed and does not include ripples.

Accordingly, it is easy to distinguish a sharp variation waveform ofreceived light intensity resulting from reflection by edges of anoriginal paper sheet 5 from a smooth waveform of received lightintensity resulting from reflection by the inner surface of the originalpressing sheet 4. Thereby, without being affected by dirt occurring onthe inner surface of the original pressing sheet 4, an output signal(indicating the intensity of the light received by the light receivingunit 12) of the light receiving unit 12 can be suitably processed. As aresult, edges of an original paper sheet 5 can be easily, preciselyrecognized.

FIG. 3 shows an example of a waveform of intensity of light reflected bythe inner surface of the original pressing sheet 4 and an original papersheet 5, and then received by the light receiving unit 12 when a lightbeam having a cross-section size according to the second embodiment isused as the light beam 6 emitted by the light-emitting diode 8 of thelight scanning unit 2. A portion A of the waveform indicates lightintensity when the light beam 6 scans the inner surface of the originalpressing sheet 4. A portion B of the waveform indicates light intensitywhen the light beam 6 scans the original paper sheet 5. A lengthindicated by C in the figure corresponds to the cross-section diameterof the light beam 6 on either the original paper sheet 5 or the originalpressing sheet 4.

With reference to FIG. 5A, an original reading apparatus in a thirdembodiment of the present invention will now be described. The originalreading apparatus in the third embodiment has a structure shown in FIGS.1A and 5, and includes a threshold setting unit 124 connected with theoriginal edge determining unit 123.

An operation of the original reading apparatus in the third embodimentwill be now described. The original edge determining unit 123 measuresvariation of light intensity of a light beam 6 received by the lightreceiving unit 12 during the first scanning operation. Based on a resultof the light intensity variation measurement, the threshold setting unit124 determine a first sharp light intensity variation in the measurementresult as an intensity variation resulting from the starting edge of theoriginal paper sheet 5 placed on the original placement table 3 beingscanned by the light beam 6.

Then, the threshold setting unit 124 obtains a difference, in theintensity of the received light, when the sharp variation occurs,between the first intensity before the sharp variation and the secondintensity after the sharp variation. The threshold setting unit 124determines an intensity value intermediate between these first andsecond intensities to be a threshold value. The thus-determinedthreshold value is used for the above-mentioned determination performedby the original edge determining unit 123 to determine the positions ofthe starting and ending edges of the original paper sheet 5.Specifically, the original edge determining unit 123 determinesinstances when the intensity received by the light receiving unit 12passes through the threshold value as being instances when the scanninglight beam 6 reaches the starting and ending edges of the original papersheet 5.

For example, with reference to FIG. 5B, in the case where the originalpaper sheet 5 is a white paper sheet, the intensity of the lightreceived by the light receiving unit 12 first sharply increases when thelight beam 6 reaches the starting edge of the paper sheet 5 in onescanning operation. Then, the threshold determining unit 124 determinesan intensity value intermediate between an intensity value immediatelybefore the sharp intensity increase and the intensity value immediatelyafter the sharp intensity increase. Then, in a second scanning operationby the light scanning unit 2, in which a scanning path may be slightlyshifted from that of the first scanning operation (by slightly shiftingthe light scanning path repeatedly, it being possible to scan the entirearea of the original placement table 3), the original edge determiningunit 123 uses the thus-determined threshold level. When the intensity ofthe received light received by the light receiving unit 12 first passesthrough the threshold value, that is, the intensity of the receivedlight increases and reaches the threshold value. Then, the originaldetermining unit 123 determines that it is an instance at which thescanning light beam 6 reaches the starting edge of the paper sheet 5.Then, also in the second scanning operation, the intensity of thereceived light received by the light receiving unit 12 again passesthrough the threshold value, that is, the intensity of the receivedlight decreases and reaches the threshold value. Then, the originaldetermining unit 123 determines that it is an instance at which thescanning light beam 6 reaches the ending edge of the paper sheet 5.

Thus, in the third embodiment, the threshold value is automaticallydetermined by the threshold setting unit 124 depending on a reflectivityof an original paper sheet 5 currently placed on the original placementtable 3. Thereby, the determined threshold value is appropriate for thereflectivity of the currently placed original paper sheet 5. As aresult, in subsequent scanning operations performed on the same papersheet 5, edges of the original paper sheet 5 can be surely, easilydetected. Thus, sure and easy original edge detection is performedwithout being affected by an optical density of a particular originalpaper sheet 5.

With reference to FIGS. 6, 7 and 8, an original reading apparatus in afourth embodiment of the present invention will now be described.Generally, the original reading apparatus in the fourth embodiment has astructure shown in FIG. 1A. The apparatus uses the above-mentionedlight-emitting diode 8 as a light source for performing a light scanningoperation. The above-mentioned single lens 9 is provided in an opticalpath between the light-emitting diode 8 and a surface of the originalpaper sheet 5.

With reference to FIG. 6, a light beam 6 is emitted by a light-emittingsurface having a diameter LR of the light-emitting diode 8, passesthrough the single lens 9 and then is incident on the surface of theoriginal paper sheet 5 with a light-beam cross section having a diameterSR. Precisely speaking, the diameter SR is a diameter which is notalways a diameter of a light-beam cross section on an actual surface ofthe original paper sheet 5 but is a diameter of the light-beam crosssection perpendicular to a direction of the optical path of the lightbeam 6. An optical path length A is provided between the light-emittingdiode 8 and the single lens 9, and an optical path length B is providedbetween the single lens 9 and the original paper sheet 5. There, a ratioof the diameter LR to the diameter SR is approximately equal to a ratioof the length A to the length B. That is, LR:SR≈A:B.

Further, a beam splitter 11 shown in FIG. 7 is provided between thesingle lens 9 and the light-emitting diode 8. The beam splitter 11, madeof a semitransparent mirror, is thus provided in the course in which alight beam 6 emitted by the light-emitting diode 8 is diverging. Thebeam splitter 11 reflects light which has been reflected by the originalpaper sheet 5 or the original pressing sheet 4, then diffused andreturned. Further, the light receiving unit (detector) 12 is providedand receives light thus reflected by the beam splitter 11. The detector12 is located so that the detector 12 acts as a light converging pointwhich is conjugate with the surface of the original paper sheet 5.

The light beam 6 caused to converge by the single lens 6 is deflected bythe above-described deflecting unit 10 and thus performs the lightscanning operation. In this case, as to be used in the deflecting unit10, a mirror which generates a non-aberration light beam 6 is morepreferable than a prism which generates astigmatism. The astigmatism ofthe prism occurs when the light beam 6 emitted from the light scanningunit 2 is incident thereon and also occurs when a reflected light beam 6reflected by either the original paper sheet 5 or the original pressingsheet 4 is incident thereon.

If a rotating mirror 13 is used in the deflecting unit 10 as shown inFIG. 8, it is preferable to provide a significant angle between arotation axis X-X' and each reflecting surface 13a. Thereby, it ispossible to provide a significant angle between the light beam emittedtoward the original paper sheet 5 and the light beam reflected by eitherthe original paper sheet 5 or the original pressing sheet 4. As aresult, it is possible to prevent a case where light reflected by areflecting surface 13a is incident on the light receiving unit 12 asnoise.

Further, in the fourth embodiment, the light-emitting diode 8 has alight-emitting surface S1 of a diameter D1 of approximately 0.3 mm. Thelight-emitting diode 8 is one which is a very popular, inexpensive itemon the market.

In the above-described structure, a light beam 6 emitted by thelight-emitting diode 8 is used for scanning the scanning surface (forexample, the surface of the original paper sheet 5) and has a desiredbeam cross-section diameter as a result of being converged by the singlelens 9. The light beam 6 is reflected by the scanning surface andreturned along the scanning optical path. The light beam 6 is thenpartially reflected by the beam splitter 11. Thereby, the light beam 6reflected by the original paper sheet 5 in the example is incident onthe light receiving unit 12 in a condition of being properly focused atan incident surface of the light receiving unit 12.

As mentioned above, the original pressing sheet 4 is in a somewhat openstate when the size of the original paper sheet 5 placed on the originalplacement table 3 is read. Therefore, the inner surface of the originalpressing sheet 4 is farther from the light-emitting diode 8 than theoriginal paper sheet 5 as shown in FIG. 7. As a result, a light beamreflected by the inner surface of the original pressing sheet 4 isincident on the light receiving unit 12 in a condition of not beingproperly focused. However, a light beam resulting from the lightscanning operation at an edge of the original paper sheet 5 is incidenton the light receiving unit 12 in the condition of being properlyfocused. Thereby, a corresponding optical signal input to the lightreceiving unit 12 has a correct value. Accordingly, it is possible tosurely recognize edges of the original paper sheet 5.

Thus, in the fourth embodiment of the present invention, it is notnecessary to use a laser diode as the light source for the lightscanning operation. Instead, the light-emitting diode 8 is used for thesame purpose. The light-emitting diode 8 used is such as that having asomewhat large light-emitting surface. As a result, fulfillment of anysafety regulation is not necessary therefor, it is easy to drive thelight-emitting diode 8, and the light-emitting diode 8 is an inexpensiveitem on the market. Further, by using an inexpensive combination of thelight-emitting diode 8 and the single lens 9, it is possible to supply alight beam having a desired light-beam cross-section diameter. Thus,costs are effectively saved.

Further, in the fourth embodiment, the light scanning operation isperformed using the beam splitter 11, having a certain NA (NumericalAperture), and thus the light beam 6 is caused to converge. Theresulting converging point is on approximately the surface of theoriginal paper sheet 5. According to this condition, a diameter of thethus-converging light beam 6 on an object, other than the original papersheet 5, for example, on the inner surface of the original pressingsheet 4, is larger as the object is farther from the light-emittingdiode 8 than the original paper sheet 5. A light beam reflected by theobject such as the original pressing sheet 4 and diffused has a largercross-section diameter. The light beam is then incident on the lightreceiving unit 12. As a result, intensity of the thus-incident lightbeam is less strong than intensity of the light beam reflected by theoriginal paper sheet 5. Therefore it is easy to distinguish the lightbeam reflected by the original paper sheet 5 from that reflected byanother object such as the original pressing sheet 4. In this case, byproviding an aperture of a small diameter on a front surface of thelight receiving unit 12, or by using the light receiving unit 12 havinga small diameter thereof, it is possible to prevent disturbance lightand to collect only light which is a light component of the beam centerand therefore has higher power.

In the fourth embodiment, the beam splitter 11 is located in theretroreflection path between the light-emitting diode 8 and the originalpaper sheet 5. As one example of this arrangement, the beam splitter 11is located between the single lens 9 and the light-emitting diode 8 asshown in FIG. 7. However, instead, it is also possible that, as shown inFIG. 9, the beam splitter 11 is located on the original paper sheet 5side of the single lens 9. In this case, a focal lens 19 is providedbetween the beam splitter 11 and the light receiving unit 12. The beamsplitter 11 reflects light which has been reflected by the originalpaper sheet 5 or the original pressing sheet 4, then diffused andreturned. The focal lens 19 converges the light beam reflected by thebeam splitter 11 so that the light beam which has been reflected by theoriginal paper sheet 5 is properly focused at the incident surface ofthe light receiving unit 12.

In the arrangement shown in FIG. 9, an additional lens, that is, thefocal lens 19 should be provided, in comparison to the arrangement shownin FIG. 7. However, similar to the arrangement shown in FIG. 7, thelight-emitting diode is used and has a somewhat large light-emittingsurface. As a result, fulfillment of any safety regulation is notnecessary therefor, it is easy to drive the light-emitting diode 8, andthe light-emitting diode 8 is an inexpensive item on the market.Further, by using an inexpensive combination of the light-emitting diode8 and the single lens 9, it is possible to supply a light beam having adesired a light-beam cross-section diameter. Thus, costs are effectivelysaved.

With reference to FIG. 10, an original reading apparatus in a fifthembodiment will now be described. Generally, the original readingapparatus in the fifth embodiment has a structure shown in FIG. 1A. Inthis embodiment, as shown in FIG. 10, a light beam 6 emitted by thelight-emitting diode 8 is caused to converge through a convergingelement (lens) 14. Then, another converging lens 15 causes the lightbeam 6 to converge. The converging light beam 6 is then used for thelight scanning operation performed on a scanning surface. In thearrangement shown in FIG. 10, a diffusing light beam from thelight-emitting diode 8 can be efficiently collected by the convergingelement 14. The collected light beam 6 is then caused to converge ontothe surface of the original paper sheet 5 through the converging lens15. Thus, it is possible to efficiently use light power output by thelight-emitting diode 8.

The other arrangement of the original reading apparatus in the fifthembodiment and functions thereof are substantially identical to those ofthe original reading apparatus in the fourth embodiment, part of whichis shown in FIG. 7.

In the embodiments shown in FIGS. 7, 9 and 10, the light path alongwhich light emitted by the light-emitting diode 8 goes and isapproximately focused on the original paper sheet 5 and also returnsfrom the original paper sheet 5 to the light receiving unit 2,substantially along the same optical axis. Such an optical system may bereferred to as a retroreflection optical system. In the retroreflectionoptical system, it is possible to substantially prevent disturbancelight, other than light originally emitted by the light-emitting diode 8and reflected by the original paper sheet 5 and the original pressingsheet 4, from incident on the light receiving unit 12. In theretroreflection optical system, substantially only light reflected by anobject present on the optical axis returns along the optical axis.

With reference to FIG. 11, an original reading apparatus in a sixthembodiment will now be described. Generally, the original readingapparatus in the sixth embodiment has a structure shown in FIG. 1A anddoes not use the retroreflection optical system. Further, as shown inFIG. 11, the original reading apparatus has a structure identical tothat shown in FIG. 10, except that a light receiving unit 16 is providedinstead of the beam splitter 11 and the light receiving unit 12 shown inFIG. 10. In the arrangement shown in FIG. 11, the light receiving unit16 is provided at an arbitrary position but out of an optical path alongwhich a light beam 6 emitted by the light-emitting diode 8 extends to anoriginal paper sheet 5. The light receiving unit 16 includes aconverging lens 17 and a detector 18. The light receiving unit 16 has awide-angle light receiving function and thus receives light reflected bythe entirety of the scanning surface. In other words, the lightreceiving unit 16 receives light reflected from any position of anoriginal paper sheet 5 placed on the original placement table 3 as longas the original paper sheet 5 is placed within and area which thedeflecting unit 10 in the light scanning unit 2 can cause a light beam 6to scan.

The converging lens 17 is such as a toroidal lens which collects lightreflected by a surface of an original paper sheet 5 and the innersurface of the original pressing sheet 4 through the entire scanningrange of the light scanning unit 2 in one scanning operation of thelight scanning unit 2. The detector 18 has a wide light-receivingsurface thereon and receives light collected by the converging lens 17.

In the arrangement shown in FIG. 11, a light beam 6 emitted by thelight-emitting diode 8 is caused to scan the surface of the originalpaper sheet 5 and the inner surface of the original pressing sheet 4through the deflecting unit 10. Light, which is reflected by the surfaceof the original paper sheet 5 and the inner surface of the originalpressing sheet 4 and does not pass through the scanning optical pathbetween the deflecting unit 10 and the original paper sheet 5 or theoriginal pressing sheet 4, is received by the light receiving unit 16.Thus, in the sixth embodiment, scattered light reflected by the originalpaper sheet 5 is used. Therefore, it is possible to locate the lightreceiving unit 16 in an arbitrary position such as a position inproximity to the original placement table 3 or the like.

With reference to FIGS. 12, 13A, 13B and 13C, an original readingapparatus in a seventh embodiment of the present invention will now bedescribed. In this apparatus, a body 1 has therein a light scanning unit2 which scans, with the light beam 6, the original paper sheet 5 from aninner side of the transparent original placement table 3. In the lightscanning unit 2, light emitted by the light-emitting diode 8 and havingseveral millimeters of a spot diameter is reflected by the beam splitter11. The reflected light is converged through the focal lens 19, and thenis used to scan the original placement table 3 through the mirror 13driven by a polygon motor 10a and thus turning. In this case, a scanningline 7 forms an arc as a result of the light beam 6 scanning with acertain incident angle to a normal to the original placement table 3.The scanning light beam 6 is reflected by the original paper sheet 5through the transparent original placement table 3. The reflectedscattered light returns through a retroreflection path through which thelight beam 6 reflected by the mirror 13 is incident on the originalpaper sheet 5. The transparent original placement table 3 also reflectsthe scanning light beam 6 and the reflected scattered light also returnsthrough the retroreflection path.

In the retroreflection path, a distance-detection light-receiving unit20 is provided. The distance-detection light-receiving unit 20 receiveslight which passes through the beam splitter 11, and outputs a signalwhich depends on a length of an incident-light path. A knife edge 21 isprovided in front of the distance-detection light-receiving unit 20 asshown in FIG. 12.

As shown in FIGS. 13A-13C, the distance-detection light-receiving unit20 includes a two-piece photodiode which has two light receiving areas20A, 20B. The two light receiving areas are arranged symmetrically witha split line which crosses a light axis of the focal lens 19. Further,an original edge determining unit 123A receives a detection signaloutput by the distance-detection light-receiving unit 20. Using thereceived detection signal, the original edge determining unit 123Adetermines a position of an edge of the original paper sheet 5 withrespect to the original placement table 3. Whether the light currentlybeing received by the distance-detection light-receiving unit 20 is thelight reflected by an edge of the original paper sheet 5 is determined,by the distance-detection light-receiving unit 20 as will be describedlater.

In this arrangement, in a condition in which the original pressing sheet4 is in an open position as shown in FIG. 12, the light emitted by thelight emitting diode 8 is used for scanning the original paper sheet 5and the original pressing sheet 4 through the light scanning unit 2. Asa result, the light is reflected by the original paper sheet 5 and theoriginal pressing sheet 4. The thus-reflected light is incident on thedistance-detection light-receiving unit 20. In addition, otherdisturbance light from room lightings and so forth is also incident onthe distance-detection light-receiving unit 20. The knife edge 21 isprovided in front of the distance-detection light-receiving unit 20 andaffects the light before it is incident on the distance-detectionlight-receiving unit 20. As a result, according to the principle of thewell-known knife edge method, a position of a spot S, shown in FIGS.13A-13C, formed by the incident light on the distance-detectionlight-receiving unit 20 varies as a length of an incident-light pathvaries. The length of an incident-light path is a length of a light paththrough which the light comes to the distance-detection light-receivingunit 20 from a source such as the original paper sheet 5, originalpressing sheet 4, or room lightings or the like from which disturbancelight is emitted.

FIG. 13A shows a position and a shape of the spot S formed on thedistance-detection light-receiving unit 20 when the length of theincident-light path is relatively short. As shown in the figure, theposition of the spot S is relatively high. FIG. 13C shows a position anda shape of the spot S formed on the distance-detection light-receivingunit 20 when the length of the incident-light path is relatively long.As shown in the figure, the position of the spot S is relatively low.FIG. 13B shows a position and a shape of the spot S formed on thedistance-detection light-receiving unit 20 when the length of theincident-light path is a middle length. As shown in the figure, theposition of the spot S is in a middle position. As shown in FIGS.13A-13C, each spot S consists of two parts, each part being formed on arespective one of the two light-receiving areas 20A, 20B of thedistance-detection light-receiving unit 20. The distance-detectionlight-receiving unit 20 has performance such that an output A or B fromeach of the two light-receiving areas 20A, 20B varies as an area of arespective part of the spot S formed thereon varies. Therefore, as thelength of the incident-light path varies, the outputs A, B from the twolight-receiving areas 20A, 20B vary, respectively. Specifically, as anarea of the part of the spot S formed on each of the two light-receivingareas 20A, 20B increases, the output thereof increases. Therefore, thedistance-detection light-receiving unit 20 uses the outputs A, B, andthus recognizes the length of the incident-light path of the lightcurrently being incident on the distance-detection light-receiving unit20.

For example, the focal lens 19, distance-detection light-receiving unit20 and knife edge 21 are positioned to have a predetermined spatialarrangement. In this condition, when the distance-detectionlight-receiving unit 20 receives the light which has been reflected fromthe original paper sheet 5 placed on the transparent original placementtable 3 and then affected by the knife edge 21 according to theprinciple of the knife edge method, the length of the incident-lightpath is relatively short. As a result, similar to the case shown in FIG.13A, an area of a part of the spot S formed on the upper light receivingarea 20A is larger than an area of the other part of the spot S formedon the lower light receiving area 20B. Thereby, a magnitude of theoutput A is larger than a magnitude of the output B (A>B).

When the distance-detection light-receiving unit 20 receives the lightwhich has been reflected from the original pressing sheet 4 in the openposition and then affected by the knife edge 21 according to theprinciple of the knife edge method, the length of the incident-lightpath is relatively large. As a result, similar to the case shown in FIG.13C, an area of a part of the spot S formed on the upper light receivingarea 20A is smaller than an area of the other part of the spot S formedon the lower light receiving area 20B. Thereby, a magnitude of theoutput A is smaller than a magnitude of the output B (A<B).

By positioning the focal lens 19, distance-detection light-receivingunit 20 and knife edge 21 as described above according to thepredetermined spatial arrangement, when the distance-detectionlight-receiving unit 20 receives other disturbance light originatingfrom room lightings and or the like and then affected by the knife edge21 according to the principle of the knife edge method, a magnitude ofthe output A is also smaller than a magnitude of the output B (A<B).This is because it can be determined that the length of theincident-light path when such disturbance light is incident is longerthan the length of the incident-light path when the light reflected bythe open-position original pressing sheet 4 is incident. Therefore, thedistance-detection light-receiving unit 20 uses a condition, in whichthe two magnitudes of the outputs A and B are equal to each other (A=B),as a threshold condition for determining whether the light currentlyincident on the distance-detection light-receiving unit 20 is the lightreflected by the original paper sheet 5 placed on the original placementtable 3. The distance-detection light-receiving unit 20 determines thatthe light currently incident on the distance-detection light-receivingunit 20 is the light reflected by the original paper sheet 5 placed onthe original placement table 3 when A>B. Then, the distance-detectionlight-receiving unit 20 outputs the detection signal.

By using this method, it is possible to positively determine whether theincident light is the light reflected by the original paper sheet 5 onthe original placement table 3, even if light intensities received bythe distance-detection light-receiving unit 20 are not remarkablydifferent between the light reflected by the original paper sheet 4 onthe original placement table 3, the light reflected by the open-positionoriginal pressing sheet 4 and other disturbance light. The detectionsignal output from the distance-detection light-receiving unit 20 andanother predetermined signal output from the light scanning unit 2 areinput to the original edge determining unit 123A. The predeterminedsignal from the light scanning unit 2 indicates a timing of the lightscanning performed thereby. Using the detection signal from thedistance-detection light-receiving unit 20, the original edgedetermining unit 123A can recognize a time when the light beam 6 isincident on an edge of the original paper sheet 5. Thus, by using thethus-detected time of the edge of the original paper sheet 5 and thetiming of the light scanning, the original edge determining unit 123Acan detect a position of the edge of the original paper sheet 5 withrespect to the original placement table 3.

With reference to FIGS. 14, 15A, 15B and 15C, an original readingapparatus in an eighth embodiment of the present invention will now bedescribed.

In this embodiment, instead of the distance-detection light-receivingunit 20 in the above-described seventh embodiment, a distance-detectionlight-receiving unit 22 is used. The distance-detection light-receivingunit 22 is also a two-piece photodiode called a `the rising-sun flag(well-known Japanese national flag) type` photodiode. Thedistance-detection light-receiving unit 22 has, as shown in FIGS.15A-15C, a central light-receiving area 22A and a peripherallight-receiving area 22B on the front surface thereof. The central andperipheral light-receiving areas 22A and 22B form a spatial arrangementof the rising-sun flag as shown in the figures. An original edgedetermining unit 123B receives a detection signal output by thedistance-detection light-receiving unit 22. Using the received detectionsignal, the original edge determining unit 123B determines a position ofan edge of the original paper sheet 5 with respect to the originalplacement table 3. Whether the light currently being received by thedistance-detection light-receiving unit 22 is the light reflected by anedge of the original paper sheet 5 is determined, by thedistance-detection light-receiving unit 22, as will be described later.

In this arrangement, in a condition in which the original pressing sheet4 is in an open position as shown in FIG. 14, the light emitted by thelight emitting diode 8 is used for scanning the original paper sheet 5and the original pressing sheet 4 through the light scanning unit 2. Asa result, the light is reflected by the original paper sheet 5 and theoriginal pressing sheet 4. The thus-reflected light is incident on thedistance-detection light-receiving unit 22. In addition, otherdisturbance light from room lightings and so forth is also incident onthe distance-detection light-receiving unit 22. According to theprinciple of the well-known beam size method, a size of a spot S, shownin FIGS. 15A-15C, formed by the incident light on the distance-detectionlight-receiving unit 22 varies as a length of an incident-light pathvaries. The length of an incident-light path is a length of a light paththrough which the light comes to the distance-detection light-receivingunit 22 from a source such as the original paper sheet 5, originalpressing sheet 4, or room lightings or the like from which disturbancelight is emitted.

FIG. 15A shows a size of the spot S formed on the distance-detectionlight-receiving unit 22 when the length of the incident-light path isrelatively short. As shown in the figure, the size of the spot S isrelatively large. FIG. 15C shows a size of the spot S formed on thedistance-detection light-receiving unit 22 when the length of theincident-light path is relatively long. As shown in the figure, the sizeof the spot S is relatively small. FIG. 15B shows a size of the spot Sformed on the distance-detection light-receiving unit 22 when the lengthof the incident-light path is a middle length. As shown in the figure,the size of the spot S is a middle size. As shown in FIGS. 15A-15C, eachspot S consists of two parts, each part being formed on a respective oneof the two light-receiving areas 22A, 22B of the distance-detectionlight-receiving unit 22. The distance-detection light-receiving unit 22has performance such that an output A or B from each of the twolight-receiving areas 22A, 22B varies as an area of a respective part ofthe spot S formed thereon varies. Therefore, as the length of theincident-light path varies, the outputs A, B from the twolight-receiving areas 22A, 22B vary, respectively. Specifically, as anarea of the part of the spot S formed on each of the two light-receivingareas 22A, 22B increases, the output thereof increases. Therefore, thedistance-detection light-receiving unit 22 uses the outputs A, B, andthus recognizes the length of the incident-light path of the lightcurrently being incident on the distance-detection light-receiving unit22.

For example, the focal lens 19 and distance-detection light-receivingunit 22 are positioned to have a predetermined spatial arrangement. Inthis condition, when the distance-detection light-receiving unit 22receives the light which has been reflected from the original papersheet 5 placed on the transparent original placement table 3, the lengthof the incident-light path is relatively short. As a result, accordingto the principle of the beam size method, similar to the case shown inFIG. 15A, a size of the spot is relatively large, and therefore an areaof a part of the spot S formed on the central light receiving area 22Ais smaller than an area of the other part of the spot S formed on theperipheral light receiving area 22B. Thereby, a magnitude of the outputA is smaller than a magnitude of the output B (A<B).

When the distance-detection light-receiving unit 22 receives the lightwhich has been reflected from the original pressing sheet 4 in the openposition, the length of the incident-light path is relatively large. Asa result, similar to the case shown in FIG. 15C, a size of the spot S isrelatively small according to the principle of the beam size method, andtherefore an area of a part of the spot S formed on the central lightreceiving area 22A is larger than an area of the other part of the spotS formed on the peripheral light receiving area 22B. Thereby, amagnitude of the output A is larger than a magnitude of the output B(A>B).

By positioning the focal lens 19 and distance-detection light-receivingunit 22 as described above according to the predetermined spatialarrangement, when the distance-detection light-receiving unit 22receives other disturbance light originating from room lightings and orthe like, a magnitude of the output A is also larger than a magnitude ofthe output B (A>B). This is because it can be determined that the lengthof the incident-light path when such disturbance light is incident islonger than the length of the incident-light path when the lightreflected by the open-position original pressing sheet 4 is incident.Therefore, the distance-detection light-receiving unit 22 uses acondition, in which the two magnitudes of the outputs A and B are equalto each other (A=B), as a threshold condition for determining whetherthe light currently incident on the distance-detection light-receivingunit 22 is the light reflected by the original paper sheet 5 placed onthe original placement table 3. The distance-detection light-receivingunit 22 determines that the light currently incident on thedistance-detection light-receiving unit 22 is the light reflected by theoriginal paper sheet 5 placed on the original placement table 3 whenA<B. Then, the distance-detection light-receiving unit 22 outputs thedetection signal.

By using this method, it is possible to positively determine whether theincident light is the light reflected by the original paper sheet 5 onthe original placement table 3, even if light intensities received bythe distance-detection light-receiving unit 22 are not remarkablydifferent between the light reflected by the original paper sheet 4 onthe original placement table 3, the light reflected by the open-positionoriginal pressing sheet 4 and other disturbance light. The detectionsignal output from the distance-detection light-receiving unit 22 andanother predetermined signal output from the light scanning unit 2 areinput to the original edge determining unit 123B. The predeterminedsignal from the light scanning unit 2 indicates a timing of the lightscanning performed thereby. Using the detection signal from thedistance-detection light-receiving unit 22, the original edgedetermining unit 123B can recognize a time when the light beam 6 isincident on an edge of the original paper sheet 5. Thus, by using thethus-detected time of the edge of the original paper sheet 5 and thetiming of the light scanning, the original edge determining unit 123Bcan detect a position of the edge of the original paper sheet 5 withrespect to the original placement table 3.

With reference to FIGS. 16, 17A, 17B and 17C, an original readingapparatus in a ninth embodiment of the present invention will now bedescribed.

In this embodiment, a distance-detection light-receiving unit 23 isused. The distance-detection light-receiving unit 23 has at least fourlight receiving areas 23A₁, 23A₂, 23B₁ and 23B₂ positioned to besymmetrical with a symmetrical center coincident with the center of thedistance-detection light-receiving unit 23, as shown in FIGS. 17A-17C.Further, in front of the distance-detection light-receiving unit 23, thefocal lens 19, the beam splitter 11 and a cylindrical lens 24 areprovided in a predetermined spatial arrangement. In this arrangement,the focal lens 19 converges received light to the center of thedistance-detection light-receiving unit 23. The cylindrical lens 24 is alens which has power only in a single direction. In this embodiment, byproviding the above-described arrangement, the length of theincident-light path is determined according to the well-known astigmaticmethod. Instead of using the cylindrical lens 24, it is possible to usea wedge prism 24A as shown in FIG. 18. In FIG. 18, an optical system inthe arrangement shown in FIG. 16, including the mirror 13, lens 19, andbeam splitter 11, is indicated as a single lens.

In this arrangement, in a condition in which the original pressing sheet4 is in an open position as shown in FIG. 16, the light emitted by thelight emitting diode 8 is used for scanning the original paper sheet 5and the original pressing sheet 4 through the light scanning unit 2. Asa result, the light is reflected by the original paper sheet 5 and theoriginal pressing sheet 4. The thus-reflected light is incident on thedistance-detection light-receiving unit 23. In addition, otherdisturbance light from room lightings and so forth is also incident onthe distance-detection light-receiving unit 23. By providing the focallens 19 and the cylindrical lens 24 in front of the distance-detectionlight-receiving unit 23, according to the principle of the well-knownastigmatism method, as shown in FIGS. 17A-17C, a shape of a spot Sformed by the incident light on the distance-detection light-receivingunit 23 varies as the length of an incident-light path varies. Thelength of an incident-light path is a length of a light path throughwhich the light comes to the distance-detection light-receiving unit 23from a source such as the original paper sheet 5, original pressingsheet 4, or room lightings or the like from which disturbance light isemitted. A similar effect can be obtained when the wedge prism 24A isused instead of the cylindrical lens 24 as shown in FIG. 18.

FIG. 16A shows a shape of the spot S formed on the distance-detectionlight-receiving unit 23 when the length of the incident-light path isrelatively short. As shown in the figure, the shape of the spot S is along circle such that the horizontal length is longer than the verticallength thereof. FIG. 17C shows a shape of the spot S formed on thedistance-detection light-receiving unit 23 when the length of theincident-light path is relatively long. As shown in the figure, theshape of the spot S is a long circle such that the vertical length islonger than the horizontal length thereof. FIG. 17B shows a shape of thespot S formed on the distance-detection light-receiving unit 22 when thelength of the incident-light path is a middle length. As shown in thefigure, the shape of the spot S is an ordinary circle. As shown in FIGS.17A-17C, each spot S consists of four parts, each part being formed on arespective one of the four light-receiving areas 23A₁, 23A₂, 23B₁ and23B₂ of the distance-detection light-receiving unit 23.

The distance-detection light-receiving unit 23 has performance such thatan output A₁, A₂, B₁ or B₂ from each of the four light-receiving areas23A₁, 23A₂, 23B₁ and 23B₂ varies as an area of a respective part of thespot S formed thereon varies. When the length of the incident-light pathis the middle length as shown in FIG. 17B, the spot S is the ordinarycircle formed at the center of the distance-detection light-receivingunit 23. Therefore, areas of parts of the spot S formed on the fourlight receiving areas 23A₁, 23A₂, 23B₁ and 23B₂, respectively, are equalto each other. As a result, A₁ =A₂ =B₁ =B₂. When the length of theincident-light path is relatively short, because the spot S is ahorizontally elongated circle and therefore areas of parts formed on thelight receiving areas 23A₁ and 23A₂ are smaller than areas of partsformed on the light receiving areas 23B₁ and 23B₂, as shown in FIG. 17A,A₁ +A₂ <B₁ +B₂. In contrast to this, when the length of theincident-light path is relatively long, because the spot S is avertically elongated circle and therefore areas of parts formed on thelight receiving areas 23A₁ and 23A₂ are larger than areas of partsformed on the light receiving areas 23B₁ and 23B₂, as shown in FIG. 17A,A₁ +A₂ >B₁ +B₂. Thus, as the length of the incident-light path varies,A₁ +A₂ and B₁ +B₂ vary respectively due to variation of the shape of thespot S.

Hereinafter, A=A₁ +A₂ ; and B=B₁ +B₂. For example, the focal lens 19,cylindrical lens 24 and distance-detection light-receiving unit 23 arepositioned to have a predetermined spatial arrangement. In thiscondition, when the distance-detection light-receiving unit 23 receivesthe light which has been reflected from the original paper sheet 5placed on the transparent original placement table 3, the length of theincident-light path is relatively short. As a result, according to theprinciple of the astigmatism method, similar to the case shown in FIG.17A, a shape of the spot S is a horizontally elongated circle, andtherefore areas of parts of the spot S formed on the horizontallyarranged light receiving areas 23A₁, 23A₂ are smaller than areas of theother parts of the spot S formed on the vertically arranged lightreceiving areas 23B₁, 23B₂. Thereby, the output A is smaller than theoutput B (A<B).

When the distance-detection light-receiving unit 23 receives the lightwhich has been reflected from the original pressing sheet 4 in the openposition, the length of the incident-light path is relatively large. Asa result, similar to the case shown in FIG. 17C, a shape of the spot Sis a vertically elongated circle according to the principle of theastigmatism method, and therefore areas of parts of the spot S formed onthe vertically arranged light receiving areas 23A₁, 23A₂ are larger thanareas of the other parts of the spot S formed on the horizontallyarranged light receiving areas 23B₁, 23B₂. Therefore, the output A islarger than the output B (A>B).

By positioning the focal lens 19, cylindrical lens 24 anddistance-detection light-receiving unit 23 as described above accordingto the predetermined spatial arrangement, when the distance-detectionlight-receiving unit 23 receives other disturbance light originatingfrom room lightings and or the like, the output A is also larger thanthe output B (A>B). This is because it can be determined that the lengthof the incident-light path when such disturbance light is incident islonger than the length of the incident-light path when the lightreflected by the open-position original pressing sheet 4 is incident.

Therefore, the distance-detection light-receiving unit 23 uses acondition, in which the two magnitudes of the outputs A and B are equalto each other (A=B), as a threshold condition for determining whetherthe light currently incident on the distance-detection light-receivingunit 23 is the light reflected by the original paper sheet 5 placed onthe original placement table 3. The distance-detection light-receivingunit 23 determines that the light currently incident on thedistance-detection light-receiving unit 23 is the light reflected by theoriginal paper sheet 5 placed on the original placement table 3 whenA<B. Then, the distance-detection light-receiving unit 23 outputs thedetection signal.

By using this method, it is possible to positively determine whether theincident light is the light reflected by the original paper sheet 5 onthe original placement table 3, even if light intensities received bythe distance-detection light-receiving unit 23 are not remarkablydifferent between the light reflected by the original paper sheet 4 onthe original placement table 3, the light reflected by the open-positionoriginal pressing sheet 4 and other disturbance light. The detectionsignal output from the distance-detection light-receiving unit 23 andanother predetermined signal output from the light scanning unit 2 areinput to the original edge determining unit 123C. The predeterminedsignal from the light scanning unit 2 indicates a timing of the lightscanning performed thereby. Using the detection signal from thedistance-detection light-receiving unit 23, the original edgedetermining unit 123C can recognize a time when the light beam 6 isincident on an edge of the original paper sheet 5. Thus, by using thethus-detected time of the edge of the original paper sheet 5 and thetiming of the light scanning, the original edge determining unit 123Ccan detect a position of the edge of the original paper sheet 5 withrespect to the original placement table 3.

With reference to FIGS. 19, 20 and 21, an original reading apparatus ina tenth embodiment of the present invention will now be described. Thisapparatus includes an original edge detecting system including aposition-detection sensor 25, such as a position sensing device (PSD),acting as distance-detecting light-receiving means. The light beam 6used for scanning through the light scanning unit 2 is reflected by theoriginal paper sheet 5 or the open-position original pressing sheet 4.The reflected light is incident on the position-detection sensor 25. Aposition on which the reflected light is incident on theposition-detection sensor 25 varies as the length of the incident-lightpath. As shown in FIG. 19, the light emitted by the light-emitting diode8 is converged by the single lens 9 and then used to scan the originalpaper sheet 5 and the original pressing sheet 4 which then reflect thescanning light. The reflected, scattered light causes an image to beformed on the position-detection sensor 25 through the focal lens 19.

In this system, actually, as shown in FIG. 20, the light reflected bythe original paper sheet 5 or the original pressing sheet 4 is incidenton the position-detection sensor 25 via the mirror 13. Theposition-detection sensor 25 is provided at a position, on a plane onwhich the light-emitting diode 8 is also provided, but different from aposition at which the light-emitting diode 8 is provided. This plane isa plane extending vertically in FIG. 20, and the light beam emitted bythe light-emitting diode 8 lies in the same plane. Further, the rotationaxis of the light scanning unit 2 also lies on the same plane.

In this arrangement, in a condition in which the original pressing sheet4 is in the open position as shown in FIG. 19, the light emitted by thelight emitting diode 8 is used for scanning the original paper sheet 5and the original pressing sheet 4 through the light scanning unit 2. Asa result, the light is reflected by the original paper sheet 5 and theoriginal pressing sheet 4. The thus-reflected light is incident on theposition-detection sensor 25. In addition, other disturbance light fromroom lightings and so forth is also incident on the position-detectionsensor 25. As shown in FIG. 21, a position of the spot S formed by theincident light on the position-detection sensor 25 varies as the lengthof the incident-light path varies.

Specifically, as the length of the incident-light path decreases, theposition at which the light is incident on the position-detection sensor25 is shifted in a direction `a`. As the length of the incident-lightpath increases, the position at which the light is incident on theposition-detection sensor 25 is shifted in a direction `b`. A voltageoutput by the position-detection sensor 25 varies as the position of thespot S formed thereon is shifted. Therefore, by measuring the voltageoutput by the position-detection sensor 25, an original edge determiningunit 123D shown in FIG. 19 can recognize the current length of theincident-light path. Further, by comparing with a predeterminedthreshold level, for example, it is possible to detect whether thecurrent incident light is light reflected by the original paper sheet 5on the transparent original placement table 3.

The position-detection sensor 25 is provided on the plane in which thelight beam emitted by the light-emitting diode 8 lies, as mentionedabove. Thereby, the spot S scans on the position-detection sensor 25linearly along a certain line segment as the length of theincident-light path varies. The position-detection sensor 25 outputs thevoltage according to the position of the spot S on theposition-detection sensor 25, as mentioned above. By using the voltage,the original edge determining unit 123D detects a time at which thelight beam 6 is incident on an edge of the original paper sheet 5 on theoriginal placement table 3. Then, by also using a signal indicating thescanning operation performed by the light scanning unit 2, the originaledge determining unit 123D can detect a position of the edge of theoriginal paper sheet 5 with respect to the original placement table 3.

Instead of using the light scanning unit 2 shown in FIGS. 17 and 18, itis also possible to provide means for moving a whole unit which includesthe light-emitting diode 8, single lens 9, focal lens 19 andposition-detection sensor 25, and thereby a scanning line 7 is formed onthe original paper sheet 5 and the original pressing sheet 4. Further,the position-detection sensor 25 is not limited to the position sensingdevice (PSD). A line-type CCD sensor or a two-dimensional CCD sensor mayalso used for the same purpose.

With reference to FIG. 22, an original reading apparatus in an eleventhembodiment of the present invention will now be described.

The apparatus includes an original edge detecting system. In thissystem, instead of using the position-detection sensor 25 in thearrangement shown in FIGS. 19 and 20, a two-dimensional CCD sensor 26 isused acting as the distance-detection light-receiving means. Thetwo-dimensional CCD sensor has thereon a two-dimensional light-receivingarea. In the arrangement of the eleventh embodiment, as the length ofthe incident-light path varies, a size, a shape, a light-intensitydistribution and so forth in a spot S formed on the two-dimensionallight-receiving area of the CCD sensor 26 as a result of the reflectedlight being incident thereon vary. The length of the incident light pathis a length between an object, which reflects the scanning lightprovided by the light scanning unit 2, and the two-dimensional CCDsensor 26.

In this system, three cases will now be considered in which objectswhich reflect the scanning light are reflection surfaces 27, 28 and 29,and thus the lengths of the incident-light paths to the two-dimentionalCCD sensor 26 are short, middle and long, respectively. A size of thespot formed on the two-dimensional CCD sensor 26 varies as a reflectionsurface used is changed between the reflection surfaces 27, 28 and 29.By detecting this spot-size variation, it is possible to positivelydetermine whether the received light comes from the reflection surfaces27, 28 or 29. By using this principle, it is also possible to positivelydetermine whether the received light comes from the original paper sheet5 or the original pressing sheet 4, or the received light is disturbancelight coming from room lightings and so forth. This is because, when thelight is light coming from the original paper sheet 5, the length of theincident-light path is relatively short. In contrast to this, when thelight is light coming from the original pressing sheet 4 or the light isdisturbance light coming from room lightings or the like, the length ofthe incident-light path is relatively long.

With reference to FIGS. 23A, 23B, 24A and 24B, an original readingapparatus in a twelfth embodiment of the present invention will now bedescribed. The apparatus includes an original edge detecting system.This system uses a rectangular lens 30 as a converging lens togetherwith the above-described two-dimensional CCD sensor 26. The rectangularlens is rectangular when viewed along the incident light direction. Therectangular lens 30 and the CCD sensor 26 are arranged appropriately sothat, when the length of the incident-light path is relatively short, asshown in FIG. 23A, a shape of the resulting spot S on the CCD sensor 26is a shape, similar to a square, but a central portion of each of foursides thereof outwardly project as shown in FIG. 23B. In contrast tothis, when the length of the incident-light path is relatively long, asshown in FIG. 24A, a shape of the resulting spot S on the CCD sensor 26is a shape, similar to a square, but a central portion of each of foursides thereof inwardly project as shown in FIG. 24B. Such a shapevariation is detected through the two-dimensional CCD sensor 26.Thereby, it is possible to positively determined whether the receivedlight comes from the original paper sheet 5 as a result of detecting thelength of the incident-light path.

With reference to FIGS. 25A, 25B, 25C, 26A, 26B, 26C and 26D, anoriginal reading apparatus in a thirteenth embodiment of the presentinvention will now be described. The apparatus includes an original edgedetecting system. The system uses a collimator lens (as shown in FIG.25A) or an aperture (as shown in FIG. 25B) which is provided in a lightpath in the system together with the above-described two-dimentional CCDsensor 26. In each of FIGS. 25A and 25B, an optical system, such as thatin the arrangement shown in FIG. 16, including the mirror 13, lens 19,and beam splitter 11, is indicated as a single lens. By providing thecollimator lens in the light path, because the diameter of thecollimator lens is limited, an outer portion of an incident light beamis eclipsed thereby. Similarly, by providing the aperture in the lightpath, an outer portion of an incident light beam is eclipsed thereby.

By using such phenomena, the system in the thirteenth embodiment has anarrangement such that, when the length of the incident-light path isrelatively short as shown in FIG. 26A, a light-intensity distribution ofthe resulting spot on the CCD sensor 26 is such as that shown in FIG.26B. In contrast to this, when the length of the incident-light path isrelatively long, as shown in FIG. 26C, a light-intensity distribution ofthe resulting spot on the CCD sensor 26 is such as that shown in FIG.26D. By using waveforms of signals output by the CCD sensor 26 such asthose shown in FIGS. 26B and 26D, it is possible to recognize thecurrent length of the incident-light path. Thereby, it is possible topositively determined whether the received light comes from the originalpaper sheet 5 as a result of detecting the length of the incident-lightpath.

The point-light-source LED (Light-Emitting Diode) shown in FIGS. 25A and25B has coherence. Due to the eclipse of the collimator lens or theaperture, a light-intensity distribution of the light beam incident onthe original paper sheet 5 or the original pressing sheet 4, after thelight beam emitted by the point-light-source LED passing through thecollimator lens or the aperture, is one such as that shown in FIG. 25C.Then, the light beam having such a light-intensity distribution, afterbeing reflected by the original paper sheet 5 or the original pressingsheet 4, is incident on the CCD sensor 26 shown in FIGS. 26A and 26C asmentioned above. When the light beam is reflected by the original papersheet 5 or the original pressing sheet 4, the light beam scatters. Whenthe reflected light beam is incident on the sensor 26 as shown in FIG.26A where the light beam is incident on the sensor short of the focalpoint thereof, the light beam has the light-intensity distribution suchas that shown in FIG. 26B which is blunt from but similar to thedistribution shown in FIG. 25C. When the reflected light beam isincident on the sensor 26 as shown in FIG. 26C where the light beam isincident on the sensor ahead of the focal point thereof, the light beamhas the light-intensity distribution such as that shown in FIG. 26Dwhich is further blunt from the distribution shown in FIG. 26B due toaberration.

In any of the above-described eleventh, twelfth and thirteenthembodiments, whether the received light comes from the original papersheet 5 is detected by using a size, a shape or a light-intensitydistribution of the resulting spot. In any of these embodiments, byfurther using a signal indicating the scanning operation performed by alight scanning unit such as the above-described unit 2, an original edgedetermining unit can detect a position of the edge of the original papersheet 5 with respect to an original placement table such as theabove-mentioned table 3.

An original reading apparatus in a fourteenth embodiment will now bedescribed. The apparatus includes an original edge detecting system. Inthis system, any one of the distance-detection light-receiving units 20,22 and 23 shown in FIGS. 12, 13A-13C, 14, 15A-15C, 16 and 17A-17C, eachunit having two or four light receiving areas provided on the frontsurface thereof may be used.

In the system, a predetermined value is subtracted from first one of theabove-mentioned output A and output B of the distance-detectionlight-receiving unit. This predetermined value is a bias component ofthe first one of the output A and output B, which bias component is anoise component, such as disturbance light, but originating from lightemitted by the light-emitting diode 8. Similarly, a predetermined valueis subtracted from a second one of the above-mentioned output A andoutput B of the distance-detection light-receiving unit. Thispredetermined value is also a bias component of the second one of theoutput A and output B, which bias component is a noise component, suchas disturbance light, but originating from light emitted by thelight-emitting diode 8. Then, the result of subtracting the biascomponent from the second one of the output A and output B is multipliedwith a predetermined coefficient. Then, the result of the multiplicationis compared with the above-mentioned result of subtracting the biascomponent from the first one of the output A and output B. Thus, whetherthe currently received light is one reflected by the original papersheet 5 is determined.

The above-mentioned bias components of the output A and output B may bedetermined either by setting predetermined fixed values or by using acurrent intensity of light emitted by the light-emitting diode 8 whichmay be monitored by a special light intensity monitor.

For example, the ninth embodiment is described under a condition wherethe arrangement using the astigmatism method, shown in FIGS. 16, 17A-17Cis used. In this example, the above-mentioned outputs A₁, A₂, B₁ and B₂of the light receiving areas 23A₁, 23A₂, 23B₁ and 23B₂ are obtained whenlight is reflected by an object located at a point of substantialinfinity. Then, the coefficient α is obtained by a ratio A/B, where A=A₁+A₂, and B=B₁ +B₂. FIG. 27 shows a variation of a value, A-αB when thelength of the incident-light path varies. A value of A-αB at a point P₁shown in the figure corresponds to an actual value when the light isreflected by the original paper sheet 5. A value of A-αB at a point P₂shown in the figure corresponds to an actual value when the light isreflected by the original pressing sheet 4. A value of A-αB at a pointP₃ shown in the figure corresponds to an actual value when the light isreflected by an object located at a point of substantial infinity ordisturbance light due to room lighting or the like.

As shown in FIG. 27, the value A-αB, at P₃, resulting when the light isreflected by an object located at a point of substantial infinity orfrom disturbance light due to room lighting or the like, is close to 0.Therefore, it is problematic that the value 0 is used as a thresholdvalue when it is determined whether or not the light is one reflected bythe original paper sheet 5. Therefore, instead of 0, a value, Pa,slightly larger than 0 is used as the threshold value. Then, when thevalue, A-αB is larger than the value Pa, it is determined that the lightis one reflected by the original paper sheet 5. When the value, A-αB issmaller than the value Pa, it is determined that the light is not onereflected by the original paper sheet 5. Thereby, it is possible tosurely detect edges of the original paper sheet 5 in the mannerdescribed above in the previously described embodiments.

In conjunction with the fourteenth embodiment, it is possible toeliminate an influence of a weak disturbance light coming from a remoteobject in a method in which a value A-B (resulting from subtracting theabove-mentioned output B from the above-mentioned output A) is obtained,and a value slightly larger than 0 as the threshold value is used forthe above-mentioned determination. However, it is possible that strongdisturbance light coming from room lightings such as fluorescent lightsor the sun is directly incident on the distance-detectionlight-receiving unit. In such a case, the light intensity is so strongthat the value A-B may be an extremely positive value or an extremelynegative value. However, a ratio A/B (resulting from dividing the outputA with the output B) may be approximately a value when the length of theincident-light path is very long, such as a case where thelight-incident path starts from a point of substantially infinity, evenif absolute values of A and B are very large, and this value isapproximately the above-mentioned α. Further, a ratio A/B obtained whenthe incident light is one reflected by the original paper sheet 5 isreferred to as β. Then, a coefficient α' may be determined such thatα<α'<β. Thereby, when A/B>α', it is determined that the incident lightis one reflected by the original paper sheet 5. When A/B<α', it isdetermined that the incident light is not one reflected by the originalpaper sheet 5. In this case, when the incident light is one reflected bythe original pressing sheet 4, A/B<α.

When this determination method is achieved, producing an electroniccircuit performing a division operation of the ratio A/B requires arelatively complicated circuit. Therefore, instead of calculating theratio A/B, the value, A-αB, is obtained. Then, as described above, whenthe value, A-αB is larger than the value Pa, it is determined that thelight is one reflected by the original paper sheet 5. When the value,A-αB is smaller than the value Pa, it is determined that the light isnot one reflected by the original paper sheet 5.

With reference to FIGS. 28, 29 and 30, an optical sensor in a fifteenthembodiment of the present invention will now be described. FIG. 28 showsan optical-path arrangement in the optical sensor, FIG. 29 shows aperspective view of the optical sensor and FIG. 30 illustrates a lightconverging condition of light emitted by a light-emitting diode andincident on a to-be-detected object.

A light-emitting diode 31 is used in the optical sensor and is a common,inexpensive one which is widely used. A diameter LR, shown in FIG. 30,of a light-emitting surface of the light-emitting diode 31 isapproximately 0.3 mm.

A light scanning mechanism 33 is provided in the optical sensor. Thelight scanning mechanism 33 deflects light emitted by the light-emittingdiode 31, and causes the light to scan for the to-be-detected object 32.The light scanning mechanism 33 includes a motor 34 and a polygon mirror35 directly coupled with a rotating shaft of the motor 34. However,another type of the light scanning mechanism 33 can be used instead. Forexample, a vibrating mirror or prism may be used to cause incident lightto scan. Alternatively, a rotating hologram disc may be used to causeincident light to scan. However, it is noted that, if the rotatinghologram disc is used, a diameter of a light beam used for the scanningoperation is larger in comparison to the case where the deflection forthe scanning operation is performed through a mirror.

Between the light-emitting diode 31 and the light scanning mechanism 33,a converging optical system 36 and a beam splitter 38 are provided. Theconverging optical system 36 converges light emitted by thelight-emitting diode 31 onto the to-be-detected object 32. The beamsplitter 38 receives light which has been reflected by theto-be-detected object 32 and then is returning along a retroreflectionpath. The beam splitter 38 reflects part of the received light. Thelight reflected by the beam splitter 38 is incident on a light receivingunit (detector) 37.

In this example, the converging optical system 36 includes a singlelens. However, instead, the converging optical system 36 may include acombination of a plurality of lenses. The converging optical system 36is located between the light-emitting diode 31 and the beam splitter 38.

Further, another converging optical system 39 is provided. Theconverging optical system 39 receives light reflected by the beamsplitter 38 and converges the received light onto the light receivingunit 37. In this example, the converging optical system 39 includes asingle lens. However, instead, the converging optical system 39 mayinclude a combination of a plurality of lenses.

In the above-described arrangement, light emitted by the light-emittingdiode 31 is caused to converge through the converging optical system 36,and performs the scanning operation through the polygon mirror 35 of thelight scanning mechanism 33. If the to-be-detected object 32 is presenton a scan line 40 shown in FIG. 29, light reflected by theto-be-detected object 32 returns through the retroreflection paththrough which the light has been incident on the to-be-detected object32. The scan line 40 is a line along which a focus of the light beamemitted from the polygon mirror 35 moves in the scanning operation.

The light reflected by the to-be-detected object is incident on thepolygon mirror 35 which then reflects the incident light to the rearsurface of the beam splitter 38. Part of the incident light is reflectedby the beam splitter 38 and received by the converging optical system 39which then converges the received light. The converged light is incidenton the light receiving unit 37. The light receiving unit 37 outputs asignal indicating intensity of the incident light. Intensity of lightreceived by the light receiving unit 37 differs between a case where thelight has been reflected by the to-be-detected object and a case wherethe light is other scattered light. Therefore, by using a predeterminedthreshold level, the received light intensity is converted into eitherone of two values, one value corresponding to the case where the lighthas been reflected by the to-be-detected object and the other valuecorresponding to the case where the light is the other scattered light.Thus, whether a to-be-detected object 32 is present in a position or notis determined. The position at which light emitted from the polygonmirror 35 is currently converging for a to-be-detected object 32 in thescanning operation is determined from a current rotation angle of thepolygon mirror 35.

In the case where whether or not a to-be-detected object is present at aposition is determined, different from a case where image informationsuch as that of characters is recognized, it is not necessary to use alight beam having a very small cross-section area. In one example, ascanning light-spot diameter SR on a to-be-detected object should be anorder of several millimeters. This scanning light-spot diameter SR isachieved as a result of the converging optical system 36 appropriatelyconverging light emitted by the light-emitting diode 31. As shown inFIG. 30, the scanning light-spot diameter SR is obtained by thefollowing equation:

    SR=LR·B/A,

where LR represents the diameter of the light-emitting surface of thelight-emitting diode 31, as mentioned above, `A` represents anoptical-path length between the light-emitting diode 31 and theconverging optical system 36, and `B` represents an optical-path lengthbetween the converging optical system 36 and the to-be-detected object32.

When this optical sensor is incorporated in an apparatus, it ispreferable that a space required for the optical sensor is small. If atotal optical-path length of the optical sensor is set to be 300 to 400mm, it is possible that light emitted by the light-emitting diode 31 isconverged on a to-be-detected object 32 with the scanning light-spotdiameter SR of several millimeters.

It is possible that a light-emitting diode on the market which has alight-emitting surface diameter of approximately 0.3 mm is used as theabove-mentioned light-emitting diode 31. A light-emitting diode on themarket which has a light-emitting surface diameter of approximately 0.3mm may not have a superior directivity and may have characteristics ofemitting light which spreads widely. Therefore, light emitted may not beused efficiently. In order to solve this problem, it is necessary to usethe lens system having a large NA (Numerical Aperture).

In the optical sensor shown in FIG. 28, as shown in the figure, lightemitted by the light-emitting diode 31 is caused to converge through theconverging optical system 36 with a relatively wide cross-section area.That is, in the course of the optical path, a cross-section area of thelight beam is relatively large. Therefore, a value of NA of the lenssystem of the optical sensor is relatively large and thereby lightemitted by the light-emitting diode 31 can be efficiently used to becomeincident on the to-be-detected object 32.

Further, the beam splitter 38 which partially reflects light reflectedby the to-be-detected object 32 is located in a position in which across-section area of light beam is relatively large. As a result, it ispossible to cause the light reflected by the to-be-detected object 32 tobe efficiently incident on the converging optical system 39 for thelight-receiving unit 37. Thereby, it is possible to improve an accuracyin detecting a to-be-detected object 32.

In the optical sensor in the fifteenth embodiment, the light-emittingdiode 31 is used as a light source which is used for detecting ato-be-detected object 32, as mentioned above. As a result, fulfillmentof any safety regulation is not necessary therefor and thus it is notnecessary to provide any device for fulfilling safety regulations.Further, the light-emitting diode is an inexpensive item on the market.Thus, costs are effectively lowered.

Further, in the optical sensor in the fifteenth embodiment, theconverging optical system 36 which causes light emitted by thelight-emitting diode 31 to converge on a to-be-detected object 32 islocated between the light-emitting diode 31 and the beam splitter 38.Further, the converging optical system 39 which causes light reflectedby a to-be-detected object 32 to converge on the light receiving unit 37is located between the beam splitter 38 and the light receiving unit 37.Thereby, the converging optical system 36 which causes the light emittedby the light-emitting diode 31 to converge on the to-be-detected object32 is separated from the converging optical system 39 which causes lightreflected by the to-be-detected object 32 to converge on the lightreceiving unit 37.

Thereby, by using a lens having a large NA value in the convergingoptical system 36 which causes light from the light-emitting diode 31 toconverge on the to-be-detected object 32, it is possible to improveefficiency in using light from the light-emitting diode 31.Simultaneously, by using a lens having a long focal length as theconverging optical system 39 which causes reflected light from theto-be-detected object 32 to converge, it is possible to cause thereflected light from the to-be-detected object 32 to have a desiredfocus on the light receiving unit 37, and to cause reflected light fromany objects other than the to-be-detected object 32 not to have adesired focus on the light receiving unit 37.

The optical sensor in the fifteenth embodiment can be applied to theoriginal reading apparatus such as that of one of the above-describedfirst through sixth embodiments of the present invention. In such acase, the optical sensor is used for detecting edges of an originalpaper sheet 5 placed on a contact glass (original placement table 3). Insuch a case, light reflected by various walls inside the apparatus otherthan the contact glass is incident on the light receiving unit 37 inaddition to reflected light from the original paper sheet 5(to-be-detected object 32). However, by determining a location and afocal length of the converging optical system 39 so that reflected lightfrom the original paper sheet 5 has a desired focus on the lightreceiving unit 37, it is possible to cause intensity of light reflectedby the original paper sheet 5 to have an especially high level. Thereby,it is possible to improve an accuracy in detecting edges of the originalpaper sheet 5. In this case, it is further effective that an aperture(not shown in the figures) is formed in a front surface of the lightreceiving unit 37.

With reference to FIG. 31, an optical sensor in a sixteenth embodimentof the present invention will now be described. FIG. 31 shows an opticalpath arrangement in the optical sensor. For elements identical to thoseof the above-described optical sensor in the fifteenth embodiment, thesame reference numerals are given and descriptions thereof will beomitted. A similar manner is also applied to a description of thesubsequent embodiment. In the sixteenth embodiment, different from thefifteenth embodiment, the converging optical system 36 is locatedbetween the beam splitter 38 and the light scanning mechanism 33.

Thereby, the common converging optical system 36 is used for causinglight emitted by the light-emitting diode 31 to converge on theto-be-detected object 32 and for causing light reflected by theto-be-detected object 32 to converge on the light receiving unit 37. Asa result, a number of the converging optical systems can be reduced toone, and thereby costs are lowered. Further, it is also possible tominiaturize the optical sensor.

With reference to FIG. 32A, an optical sensor in a seventeenthembodiment of the present invention will now be described. FIG. 32Ashows an optical path arrangement of the optical sensor. In this opticalsensor, light from the light-emitting diode 31 is caused to converge bythe converging optical system 36, and is used for the scanning operationon a to-be-detected object 32 through the polygon mirror 35 of the lightscanning mechanism 33. The converging optical system 39 is located in areflected-light optical path which is different from the scanning-lightoptical path along which the light scanning operation with light fromthe light-emitting diode 31 is performed on the to-be-detected object32. The converging optical system 39 causes light reflected by theto-be-detected object 32 to converge and to be incident on the lightreceiving unit 37.

Also in this arrangement, similar to cases of above-describedembodiments, an inexpensive light-emitting diode on the market is usedas the light-emitting diode 31 and thereby a desired light-spot(light-beam cross-section) diameter appropriate for a to-be-detectedobject 32 can be provided. Further, in the seventeenth embodiment,different from the above-described fifteenth and sixteenth embodiments,no beam splitter is used in the optical path from the light-emittingdiode 31 to the to-be-detected object 32, as shown in FIG. 32A. In thearrangement shown in FIG. 32A, reflected light from the to-be-detectedobject 32 is not partially reflected but is directly incident on theconverging optical system 39 for the light receiving unit 37. As aresult, it is possible to efficiently use light emitted by thelight-emitting diode 31.

In the arrangement shown in FIG. 32A, scattered light reflected by theto-be-detected object 32 is used, and disturbance light may also beincident on the light receiving unit 37 in relation to a locationthereof. However, light reflected by the to-be-detected object 32 afterbeing emitted by the light-emitting diode 31 is incident on the lightreceiving unit 37 without fail. Therefore, a method can be applied, inwhich the light-emitting diode 31 is intermittently activated, andwhether or not a to-be-detected object 32 is present in a position canbe accurately detected by using a difference between an intensity oflight received by the light receiving unit 37 when the light-emittingdiode 31 emits light and another intensity of light received by thelight receiving unit 37 when the light-emitting diode 31 does not emitlight.

As shown in FIG. 32B, due to a general property of disturbance light, anintensity of received light resulting from the disturbance light doesnot substantially vary and substantially has a constant value althoughlight is intermittently emitted from the light-emitting diode 31 asmentioned above. The disturbance light is light which results from lightwhich is emitted by various source such as the sun, room lighting of anoffice room and so forth including the light-emitting diode 31 beingrandomly reflected by various things other than the to-be-detectedobject 32. In contrast to this, an intensity of received light which hasbeen reflected by the to-be-detected object 32 clearly varies accordingto the intermittent light emitted by the light-emitting diode 31. Thus,when the light-emitting diode 31 emits light to the to-be-detectedobject 32, a light intensity resulting from the emitted light beingreflected by the to-be-detected object 32 is added to the approximatelyconstant light intensity due to the disturbance light. When no light isemitted by the light-emitting diode 31, no intensity is added to theapproximately constant light intensity due to the disturbance light.Therefore, variation of the received light intensity forms a pulsewaveform according to the intermittent light emitting by thelight-emitting diode 31, as shown in FIG. 32B.

The embodiments of the present invention have been described forindividually embodying concepts of the present invention. However, it isalso possible to embody the present invention in a manner in which aplurality of concepts of the present invention are combined. Forexample, the method of any of the first and third embodiments fordetermining an instance when an edge of an original paper sheet isscanned can be combined with any of the arrangements shown in FIGS. 6,7, 8, 9, 10, 28, 30, 31 and 32. As mentioned above, any optical sensordescribed above can be used for determining edges of an original papersheet treated as a to-be-detected object.

Further, the present invention is not limited to the above-describedembodiments, and variations and modifications may be made withoutdeparting from the scope of the present invention.

What is claimed is:
 1. An original edge detecting system comprising:anoriginal placement table, on which an original sheet is placed; originalscanning means for causing a light beam to scan the original sheetplaced on said original placement table; light receiving means forreceiving a light beam which has been reflected by the original sheetplaced on said original placement table after being emitted by saidoriginal scanning means; and original edge determining means formonitoring light intensity of the light beam received by said lightreceiving means, said original edge determining means determining thatthe light beam currently being received by said light receiving means isa light beam reflected by an edge of the original sheet placed on saidoriginal placement table when a significant variation is detected in thelight intensity either for the first time or for the last time in onescanning operation of said original scanning means.
 2. The original edgedetecting system according to claim 1, further comprising an originalpressing sheet for having the original sheet inserted between saidoriginal pressing sheet and said original placement table,wherein:one ofsaid original pressing sheet and said original placement table issubstantially transparent, and through the transparent one said originalscanning means causes the light beam to scan the original sheet insertedbetween said original pressing sheet and said original placement table;and a diameter of a cross section of the light beam emitted by saidoriginal scanning means is, at an incident surface of the originalsheet, larger than an interval of dirty spots which possibly occur atintervals on the other one of said original pressing sheet and saidoriginal placement table.
 3. The original edge detecting systemaccording to claim 1, wherein a diameter of a cross section of the lightbeam emitted by said original scanning means is not less than 2 mm at anincident surface of the original sheet.
 4. The original edge detectingsystem according to claim 1, further comprising threshold setting meansfor setting a threshold value with which said original edge determiningmeans determines whether or not the light beam currently being receivedby said light receiving means is the light beam reflected by the edge ofthe original sheet placed on said original placement table,saidthreshold setting means setting the threshold value using a differencein the light intensity of the light beam received by said lightreceiving means when the significant variation occurs in the receivedlight intensity for the first time in the first scanning of the originalsheet.
 5. The original edge detecting system according to claim 1,wherein:said original scanning means uses a light-emitting diode as alight source of the light beam, and a single lens for converging thelight beam on the original sheet, a ratio of a diameter of alight-emitting surface of said light-emitting diode to a diameter of across section of the light beam at a surface of the original sheet beingapproximately equal to a ratio of an optical-path length between saidlight-emitting diode and said single lens to an optical-path lengthbetween said single lens and the original sheet; and a beam splitter islocated in a course of a retroreflection path between the surface of theoriginal sheet and said light-emitting diode, said beam splitterpartially reflecting light which has been reflected by the originalsheet, said light receiving means, which receives light reflected bysaid beam splitter, being located at a position which is anapproximately conjugate converging point with respect to the surface ofthe original sheet.
 6. The original edge detecting system according toclaim 5, further comprising converging means, in addition to said singlelens, for converging the light beam emitted by the light-emitting diode,the light being incident on said single lens after converging throughsaid converging means.
 7. The original edge detecting system accordingto claim 1, wherein said light receiving means is provided at anarbitrary position but out of an optical path along which the light beamemitted by said light-emitting diode extends to the original sheet;andsaid light receiving means serves a wide-angle light receivingfunction and thus receives light reflected by the entirety of thescanning surface.